MAP2K1 and MAP3K1 mutations in langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is now understood to be a neoplastic disease in which over 50% of cases have somatic activating mutations of BRAF. However, the extracellular signal‐related (ERK) pathway is activated in all cases including those with wild type BRAF alleles. Here, we applied a targeted massively parallel sequencing panel to 30 LCH samples to test for the presence of additional genetic alterations that might cause ERK pathway activation. In 20 BRAF wild type samples, we found 3 somatic mutations in MAP2K1 (MEK1) including C121S and C121S/G128D in the kinase domain, and 56_61QKQKVG>R, an in‐frame deletion in the N‐terminal regulatory domain. All three variant proteins constitutively phosphorylated ERK in in vitro kinase assays. The C121S/G128D and 56_61QKQKVG>R variants were resistant to the mitogen‐activated protein kinase kinase (MEK) inhibitor trametinib in vitro. Within the entire sample set, we found 3 specimens with mutations in MAP3K1 (MEKK1), including two truncation mutants, T779fs and T1481fs; T1481fs encoded an unstable and nonfunctional protein when expressed in vitro. T779fs was present in a specimen carrying BRAF V600E. The third variant was a single nucleotide substitution, E1286V, which was fully functional and is likely a germline polymorphism. These results indicate that LCH cells can harbor additional genetic alterations in the RAS‐RAF‐MEK pathway which, in the case of MAP2K1, may be responsible for ERK activation in a wild type BRAF setting. The resistance of some of these variants to trametinib may also have clinical implications for the combined use of RAF and MEK inhibitors in LCH. © 2015 Wiley Periodicals, Inc.     

Up-regulation of urinary-type plasminogen activator correlates with high-risk papillary thyroid carcinoma with BRAFV600E mutation and its possible molecular mechanism

The aim of the present study is to investigate the relationship between urinary-type plasminogen activator (uPA) expression and clinicopathological features in papillary thyroid carcinoma (PTC) and to determine the signal transduction of PTC cells in vitro.PTC tissues from 42 patients were analyzed for the expression of uPA and the BRAF^V600E mutation. BCPAP, a PTC cell line harboring the BRAF^V600E mutation, was used to study MAPK signaling. PCR and direct sequencing were applied to analyze BRAF^V600E mutation status. uPA mRNA expression was measured using a quantitative RT-PCR method, and uPA protein was localized using an immunohistochemical method. The ERK protein status was detected by Western blot analysis.uPA gene expression was significantly increased in PTC tissues as compared to the corresponding non-tumor tissues. Furthermore, the up-regulation of uPA mRNAs was correlated with high-risk clinicopathological features, including extrathyroid invasion, loss of cellular polarity/cohesiveness, and the BRAF^V600E mutation. Marked dephosphorylation of ERK1/2 and down-regulation of uPA expression were detected when BCPAP was treated with a MEK inhibitor, U0126.MEK inhibitors might be a potential treatment strategy for aggressive PTC with BRAF^V600E through inhibition of uPA expression.     

KSR is a scaffold required for activation of the ERK/MAPK module

Mechanisms that regulate signal propagation through the ERK/MAPK pathway are still poorly understood. Several proteins are suspected to play critical roles in this process. One of these is Kinase Suppressor of Ras (KSR), a component previously identified in RAS-dependent genetic screens in Drosophila and Caenorhabditis elegans. Here, we show that KSR functions upstream of MEK within the ERK/MAPK module. In agreement with this, we found that KSR facilitates the phosphorylation of MEK by RAF. We further show that KSR associates independently with RAF and MEK, and that these interactions lead to the formation of a RAF/MEK complex, thereby positioning RAF in close proximity to its substrate MEK. These findings suggest that KSR functions as a scaffold that assembles the RAF/MEK functional pair.     

Therapeutic potential of MEK inhibition in acute myelogenous leukemia: rationale for “vertical” and “lateral” combination strategies

In hematological malignancies, constitutive activation of the RAF/MEK/ERK pathway is frequently observed, conveys a poor prognosis, and constitutes a promising target for therapeutic intervention. Here, we investigated the molecular and functional effects of pharmacological MEK inhibition in cell line models of acute myeloid leukemia (AML) and freshly isolated primary AML samples. The small-molecule, ATP-non-competitive, MEK inhibitor PD0325901 markedly inhibited ERK phosphorylation and growth of several AML cell lines and approximately 70?% of primary AML samples. Growth inhibition was due to G(1)-phase arrest and induction of apoptosis. Transformation by constitutively active upstream pathway elements (HRAS, RAF-1, and MEK) rendered FDC-P1 cells exquisitely prone to PD0325901-induced apoptosis. Gene and protein expression profiling revealed a selective effect of PD0325901 on ERK phosphorylation and compensatory upregulation of the RAF/MEK and AKT/p70( S6K ) kinase modules, potentially mediating resistance to drug-induced growth inhibition. Consequently, in appropriate cellular contexts, both "vertical" (i.e., inhibition of RAF and MEK along the MAPK pathway) and "lateral" (i.e., simultaneous inhibition of the MEK/ERK and mTOR pathways) combination strategies may result in synergistic anti-leukemic effects. Overall, MEK inhibition exerts potent growth inhibitory and proapoptotic activity in preclinical models of AML, particularly in combination with other pathway inhibitors. Deeper understanding of the molecular mechanisms of action of MEK inhibitors will likely translate into more effective targeted strategies for the treatment of AML.     

Identification of frequent BRAF copy number gain and alterations of RAF genes in chinese prostate cancer

We recently found that TMPRSS2:ERG fusion genes and PTEN loss, which are common in Western prostate cancers are infrequent in Chinese cases. As previous studies indicated a higher frequency of RAS and BRAF mutation rates in Eastern Asian than in Western prostate cancers and fusion genes involving the RAF family genes BRAF and RAF1 were recently identified in prostate cancer in the American population, we investigated BRAF and RAF1 alterations in Chinese prostate cancer. Using fluorescence in situ hybridization, we found that BRAF was truncated in five of 200 informative Chinese cases (2.5%) and that RAF1 was truncated in three of 204 informative cases (1.5%) and genomic rearrangements of these genes were significantly correlated with high Gleason scores (>7; P < 0.01) and have a trend to appear in high clinical stage disease. A high frequency of BRAF and RAF1 copy number gain was found (29 and 15%, respectively). BRAF copy number gain in Chinese cancers was significantly higher than in UK cases (9.2%)(P < 0.001) and correlated with a number of clinical parameters. High‐level expression of BRAF was found by immunohistochemistry in Chinese cancer samples compared with adjacent nonmalignant epithelial cells, which was correlated with high BRAF copy number. We also identified KRAS codon 12 mutations in three of 96 Chinese cases, no BRAF V600E mutations were observed. Our finding suggests that the activation of the RAS/RAF/MEK/ERK pathway may be frequent in Chinese prostate cancer, with RAF gene copy number gain potentially being the main contributor. © 2012 Wiley Periodicals, Inc.     

Effect of a hot water extract of Chlorella vulgaris on proliferation of IEC-6 cells

Chlorella vulgaris, a unicellular microalgae, exerts various biological effects; however their effect on proliferation signaling pathways in normal cells has not been studied. We investigated the effect of hot water extracts of Chlorella vulgaris (CVE) on cell proliferation and related signaling pathways in rat intestinal epithelial cells (IEC-6). CVE increased the expression of insulin-like growth factor-I receptor (IGF-IR) and the phosphorylation of focal adhesion kinase (FAK) and Src. In addition, CVE induced activation of the mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/Akt pathways. We verified the increased phosphorylation of extracellular-signal-related kinase (ERK) and Akt and the increased expression of the PI3K regulatory subunit p85. CVE also influenced the canonical Wnt pathway through increased expression of the nuclear β-catenin, cyclin D1. Tyr-397 of FAK mediates interactions with Src homology?2 (SH2) domains in a number of other signaling proteins, including PI3K, PLC-γ, Shc, Grb7, Src and Nck2. Because CVE induced FAK activation, FAK may affect the Wnt pathway. Addition of a FAK inhibitor decreased the expression of nuclear β-catenin, cyclin D1 and c-myc, and increased the expression of cytosolic β-catenin. We conclude that CVE stimulated proliferation of IEC-6 cells via the MAPK, PI3K/Akt and canonical Wnt pathways, and that this affected the canonical Wnt pathway.     

Germline mutations of MEK in cardio-facio-cutaneous syndrome are sensitive to MEK and RAF inhibition: implications for therapeutic options

Cardio-facio-cutaneous (CFC) syndrome is a sporadic developmental disorder characterized by distinctive craniofacial features, heart defects, mental retardation and ectodermal abnormalities. We recently reported missense germline mutations in the genes MEK1 and MEK2 in patients with CFC. These mutations, including F53S and Y130C MEK1, and F57C MEK2, are the first naturally occurring mutations to be identified in these genes. This study reports data concerning the biochemical functions of the novel mutants, as well as the roles of these MEK genes in the MAPK signaling cascade. Our CFC MEK variants cannot induce ERK unless they are phosphorylated by RAF at two key serine residues in the regulatory loop. When we replaced the serine residues with alanines, ERK phosphorylation was significantly reduced in the presence of RAF. We did find that F57C MEK2 activation was less dependent on RAF signaling than the other mutants. This difference results in F57C MEK2 being resistant to the selective RAF inhibitor SB-590885. All three mutants are sensitive to the MEK inhibitor U0126. The majority of CFC cases result from mutations in B-RAF. A recent report indicates the possibility that cancer cells with activated B-RAF have enhanced, selective sensitivity to MEK inhibitors. Thus, regardless of mutations identified in an individual with CFC, MEK inhibition is a potential therapeutic approach for this population.     

The extended spectrum of RAS‐MAPK pathway mutations in colorectal cancer

Current clinical guidelines recommend mutation analysis for select codons in KRAS and NRAS exons 2, 3, and 4 and BRAF V600E to guide therapy selection and prognostic stratification in advanced colorectal cancer. This study evaluates the impact of extended molecular testing on the detection of RAS‐MAPK pathway mutations. Panel next‐generation sequencing results of colorectal cancer specimens from 5795 individuals from the American Association for Cancer Research Project Genomics Evidence Neoplasia Information Exchange (AACR Project GENIE) were included. Mutations in RAS‐MAPK pathway genes were analyzed and functionally annotated. Colorectal cancers had recurrent pathogenic pathway activating mutations in KRAS (44%), NRAS (4%), HRAS (<1%), BRAF (10%), MAP2K1 (1%), RAF1 (<1%), and PTPN11 (<1%). The proportion of colorectal cancers with pathogenic RAS pathway mutations was 37% when only KRAS codon 12 and 13 mutations were considered, 46% when also including select KRAS and NRAS exons 2, 3, and 4 mutations, 53% when including BRAF V600E mutations, and 56% when including all pathogenic mutations. Panel next‐generation sequencing testing identifies additional RAS‐MAPK pathway driver mutations beyond current guideline recommendations. These mutations have potential implications in treatment selection for patients with advanced colorectal cancer.     

Porphyromonas gingivalis Lipopolysaccharide Activates Canonical Wnt/β-Catenin and p38 MAPK Signalling in Stem Cells from the Apical Papilla

As dental precursor cells, stem cells from the apical papilla (SCAP) are capable of forming roots and undergoing apexogenesis, which are impaired upon exposure to bacterial infection. Porphyromonas gingivalis is a common Gram-negative bacterium that is involved in pulpal and periapical infection. The purpose of this study was to investigate the effects of P. gingivalis lipopolysaccharide (LPS) on the Wnt/β-catenin and p38 mitogen-activated protein kinase (MAPK) signalling pathways in SCAP. As indicated by the IL-1β and TNF-α mRNA levels, P. gingivalis LPS induced the expression of pro-inflammatory cytokines in a dose-dependent manner. In addition, activation of the p38 MAPK and Wnt/β-catenin pathways was confirmed by the augmentation of phospho-p38 and β-catenin protein expression and increased expression of c-myc and cyclin D1 mRNA. Despite no significant increase in β-catenin mRNA expression, increased phosphorylation of glycogen synthase kinase (GSK)-3β suggested that GSK-3β was responsible for the accumulation of β-catenin in the cytoplasm and translocation to the nucleus. Previous studies have shown that GSK-3β plays a critical role in crosstalk between the Wnt/β-catenin and p38 MAPK pathways. In the present study, we showed that the level of p38 phosphorylation decreased upon pretreatment with a p38 MAPK inhibitor for 1 h before stimulating SCAP with 10 μg/ml P. gingivalis LPS. However, the levels of GSK-3β and β-catenin phosphorylation in the cytoplasm and nucleus were not significantly altered. Our results suggest that the p38 MAPK and canonical Wnt/β-catenin signalling pathways are activated by P. gingivalis LPS in SCAP, but we have no evidence that p38 MAPK is upstream of GSK-3β in the Wnt/β-catenin signalling pathway.     

Epithelial to mesenchymal transition in early stage endometrioid endometrial carcinoma

Epithelial to mesenchymal transition is thought to be implicated in tumor invasion and metastasis. To investigate its role in myometrial invasion, samples from 42 stage I (confined to the corpus) endometrioid endometrial carcinomas were analyzed. All E-cadherin repressors (SNAI1, SNAI2 (SLUG), ZEB1, HMGA2, and TWIST1) had a higher expression in endometrioid endometrial carcinomas than in normal endometrium (P < .0001), whereas CDH1 (E-cadherin gene) tended to be lower. In comparison with nonmyoinvasive (stage IA) tumors, those with deep myometrial invasion (stage IC) had increased messenger RNA expression of SLUG, ZEB1, and HMGA2 (P < .001). Furthermore, samples from the myoinvasive front of deeply invasive tumors had higher levels of SLUG, ZEB1, and HMGA2 than the corresponding superficial samples. Immunohistochemical analysis of these cases revealed that the decrease in E-cadherin was concordant with an increase in Snail and Twist protein expression. Trying to induce epithelial to mesenchymal transition in endometrioid endometrial carcinomas, we initially produced persistent activation of this pathway in Ishikawa cells. The cell line was infected with lentiviruses carrying the V600E mutation of BRAF, inducing loss of β-catenin, E-cadherin, and cytokeratin and increase in vimentin and Snail. These changes were mediated by ERK1/2 phosphorylation, which was also increased at the myoinvasive front. Furthermore, MEK1/2 inhibitor UO126 reversed the mesenchymal phenotype. Our findings suggest that epithelial to mesenchymal transition regulators are implicated in myometrial invasion of endometrioid endometrial carcinoma and may be potential therapeutic targets through the MAPK/ERK pathway.     

An immunohistochemical and genetic study of BRAFV600E mutation in Japanese patients with ameloblastoma

Ameloblastoma is an odontogenic tumor of the jaw. It most frequently occurs in the mandible, and less often in the maxilla. Mandibular ameloblastoma harbors a BRAF mutation that causes a valine (V) to glutamic acid (E) substitution at codon 600 (BRAF^V600E). We examined specimens from 32 Japanese patients to detect the prevalence of the BRAF^V600E mutation, and to evaluate the relationship between immunohistochemical (IHC) expression and genetic results, of BRAF^V600E+ ameloblastoma. Among the 32 cases, 22 (69%) were IHC positive for BRAF^V600E protein, and 10 (31%) were IHC negative; and polymerase chain reaction showed 16 of 21 tested cases (76%) carried the BRAF^V600E mutation. Our findings indicate that that samples that stain IHC positive for BRAF^V600E protein are more likely to carry the BRAF^V600E mutation. These results support assessments for BRAF mutations, and the use of BRAF inhibitors as targeted therapy for ameloblastoma in Japanese patients.     

MEK-ERK pathway modulation ameliorates pulmonary fibrosis associated with epidermal growth factor receptor activation

Pulmonary fibrosis remains a significant public health burden with no proven therapies. The mitogen-activated protein kinase (MAPK)/MAPK kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling cascade is a major pathway controlling cellular processes associated with fibrogenesis, including growth, proliferation, and survival. Activation of the MAPK/ERK pathway is detected in the lungs of human fibrosis samples; however, the effect of modulating the pathway in vivo is unknown. Overexpression of transforming growth factor (TGF)-α in the lung epithelium of transgenic mice causes a progressive pulmonary fibrosis associated with increased MEK/ERK activation localized primarily in mesenchymal cells. To determine the role of the MEK pathway in the induction of TGF-α-induced lung fibrosis, TGF-α was overexpressed for 4 weeks while mice were simultaneously treated with the specific MEK inhibitor, ARRY-142886 (ARRY). Treatment with ARRY prevented increases in lung cell proliferation and total lung collagen, attenuated production of extracellular matrix genes, and protected mice from changes in lung function. ARRY administered as a rescue treatment after fibrosis was already established inhibited fibrosis progression, as assessed by lung histology, changes in body weights, extracellular matrix gene expression, and lung mechanics. These findings demonstrate that MEK inhibition prevents progression of established fibrosis in the TGF-α model, and provides proof of concept of targeting the MEK pathway in fibrotic lung disease.     

Zeste基因增强子同源物2通过调控Wnt/β-catenin信号通路影响脑胶质瘤细胞凋亡

目的:探讨zeste基因增强子同源物2(EZH2)通过调控Wnt/β-catenin信号通路对脑胶质瘤细胞凋亡的影响。方法:以RT-q PCR和Western blot检测胶质瘤U87、H4和U251细胞及正常人脑星形细胞(NHA)中EZH2的表达水平。在H4细胞中转染EZH2 siRNA和siRNA control,MTT测定细胞活力,流式细胞术测定细胞凋亡,分光光度计法检测caspase-3的活性,Western blot检测Wnt/β-catenin信号通路中关键蛋白β-连环蛋白(β-catenin)和下游靶分子c-Myc的蛋白表达。用Wnt/β-catenin信号通路激活剂处理转染EZH2 siRNA的H4细胞,流式细胞术测定细胞凋亡,Western blot测定β-catenin和c-Myc的表达。结果:胶质瘤U87、H4和U251细胞中EZH2的mRNA和蛋白水平均明显高于NHA(P0.05),并且H4细胞中EZH2 mRNA和蛋白水平高于U87和U251细胞(P0.05)。EZH2 siRNA可以明显下调H4细胞中EZH2的mRNA和蛋白水平。EZH2表达下调后的H4细胞从48 h开始细胞活力降低,并且细胞凋亡率也明显升高,细胞中caspase-3活性也明显升高(P0.05),同时EZH2表达下调还可以抑制β-catenin和c-Myc的表达。Wnt/β-catenin信号通路的激活剂可以减少EZH2诱导的H4细胞凋亡,降低细胞中caspase-3的活性。结论:EZH2在脑胶质瘤细胞中过度表达,下调其表达可以通过抑制Wnt/β-catenin信号通路的激活而诱导胶质瘤细胞凋亡。     

Activation of the ERK/MAPK pathway: a signature genetic defect in posterior fossa pilocytic astrocytomas

We report genetic aberrations that activate the ERK/MAP kinase pathway in 100% of posterior fossa pilocytic astrocytomas, with a high frequency of gene fusions between KIAA1549 and BRAF among these tumours. These fusions were identified from analysis of focal copy number gains at 7q34, detected using Affymetrix 250K and 6.0 SNP arrays. PCR and sequencing confirmed the presence of five KIAA1549–BRAF fusion variants, along with a single fusion between SRGAP3 and RAF1. The resulting fusion genes lack the auto‐inhibitory domains of BRAF and RAF1, which are replaced in‐frame by the beginning of KIAA1549 and SRGAP3, respectively, conferring constitutive kinase activity. An activating mutation of KRAS was identified in the single pilocytic astrocytoma without a BRAF or RAF1 fusion. Further fusions and activating mutations in BRAF were identified in 28% of grade II astrocytomas, highlighting the importance of the ERK/MAP kinase pathway in the development of paediatric low‐grade gliomas. Copyright © 2009 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Synergistic anti-proliferative effects of mTOR and MEK inhibitors in high-grade chondrosarcoma cell line OUMS-27

Chondrosarcoma is a malignant bone tumor that produces cartilaginous neoplastic tissue. Owing to the absence of an effective adjuvant therapy, high-grade chondrosarcoma has a poor prognosis. Therefore, it is important to develop an effective adjuvant therapy to prevent the recurrence and metastasis. Mammalian target of rapamycin (mTOR), a central regulator of cell growth, metabolism, proliferation, and survival, is considered an important target for anticancer drug development. The mitogen activated protein kinase (MAPK) pathway is another highly implicated cellular pathway in cancer and is thought to have compensatory effects in response to the inhibition of the phosphatidylinositol-3-kinase (PI3K)/Akt/mTOR signaling pathway. We investigated the mechanism of anti-proliferative effect of the mTOR inhibitor rapamycin and MAPK/ERK (MEK) inhibitor PD 0325901, and the combined effect of rapamycin and PD 0325901 on human chondrosarcoma cell line (OUMS-27). Combination therapy with rapamycin and PD 0325901 showed a stronger anti-proliferative effect on OUMS-27 cells than rapamycin monotherapy. We confirmed that the dual inhibition of the PI3K/Akt/mTOR and RAF/MEK/ERK signaling pathways had synergistic anti-proliferative effects in OUMS-27. Our results suggest that combination therapy of mTOR and MEK inhibitor could be an effective therapeutic approach against chondrosarcoma.     

Reactivation of Kaposi's sarcoma-associated herpesvirus from latency requires MEK/ERK, JNK and p38 multiple mitogen-activated protein kinase pathways

Lytic replication of Kaposi's sarcoma-associated herpesvirus (KSHV) promotes the progression of Kaposi's sarcoma (KS), a dominant malignancy in patients with AIDS. While 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced KSHV reactivation from latency is mediated by the protein kinase C delta and MEK/ERK mitogen-activated protein kinase (MAPK) pathways, we have recently shown that the MEK/ERK, JNK and p38 MAPK pathways modulate KSHV lytic replication during productive primary infection of human umbilical vein endothelial cells [Pan, H., Xie, J., Ye, F., Gao, S.J., 2006. Modulation of Kaposi's sarcoma-associated herpesvirus infection and replication by MEK/ERK, JNK, and p38 multiple mitogen-activated protein kinase pathways during primary infection. J. Virol. 80 (11), 5371-5382]. Here, we report that, besides the MEK/ERK pathway, the JNK and p38 MAPK pathways also mediate TPA-induced KSHV reactivation from latency. The MEK/ERK, JNK and p38 MAPK pathways were constitutively activated in latent KSHV-infected BCBL-1 cells. TPA treatment enhanced the levels of activated ERK and p38 but not those of activated JNK. Inhibitors of all three MAPK pathways reduced TPA-induced production of KSHV infectious virions in BCBL-1 cells in a dose-dependent fashion. The inhibitors blocked KSHV lytic replication at the early stage(s) of reactivation, and reduced the expression of viral lytic genes including RTA, a key immediate-early transactivator of viral lytic replication. Activation of MAPK pathways was necessary and sufficient for activating the promoter of RTA. Furthermore, we showed that the activation of RTA promoter by MAPK pathways was mediated by their downstream target AP-1. Together, these findings suggest that MAPK pathways might have general roles in regulating the life cycle of KSHV by mediating both viral infection and switch from viral latency to lytic replication.     

Alterations of the BRAF gene in thyroid tumors

BRAF belongs to the RAF family of protein kinases that are important components of the MAPK signaling pathway mediating cell growth, differentiation and survival. Activating point mutation of the BRAF gene resulting in V600E (previously designated as V599E) is a common event in thyroid papillary carcinoma, being found in approx 40% of this tumor. It has strong association with classical papillary carcinoma and tall cell and possibly Warthin-like variants. This mutation also occurs in thyroid poorly differentiated and anaplastic carcinomas, usually those containing areas of papillary carcinoma. Alterations in the BRAF gene do not overlap with RAS mutations and RET/PTC rearrangement, indicating that activation of one of the effectors of the MAPK pathway is sufficient for papillary thyroid carcinogenesis. Recently, another mechanism of BRAF activation has been identified, which involves chromosome 7q inversion that results in the AKAP9-BRAF fusion. It is rare in sporadic papillary carcinomas and is more common in tumors associated with radiation exposure. Yet another mechanism of BRAF activation may involve copy number gain, which is seen in a significant portion of thyroid follicular tumors of both conventional and oncocytic (Hürthle cell) types.     

p21 protein-activated kinase 1 is associated with severe regressive autism,and epilepsy

The p21-activated kinase (PAK) family of proteins function as key effectors of RHO family GTPases in mammalian cells to regulate many pathways including Ras/Raf/MEK/ERK and Wnt/β-catenin, amongst others. Here we report an individual with a novel autosomal dominant disorder characterized by severe regressive autism, intellectual disability, and epilepsy. Exome sequencing of the proband and her parents revealed a de novo variant in the PAK1 gene ([NM_001128620] c.362C>T/p.Pro121Leu). Studies in patient cells showed a clear effect on PAK1 protein function, including altered phosphorylation of targets (JNK and ERK), decreased abundance of β-catenin, and concomitant altered expression downstream of these key regulators. Our findings add PAK1 to the list of PAK proteins and kinases which when mutated cause rare genetic diseases.