Palb2 synergizes with Trp53 to suppress mammary tumor formation in a model of inherited breast cancer

Germ-line mutations in PALB2 lead to a familial predisposition to breast and pancreatic cancer or to Fanconi Anemia subtype N. PALB2 performs its tumor suppressor role, at least in part, by supporting homologous recombination-type double strand break repair (HR-DSBR) through physical interactions with BRCA1, BRCA2, and RAD51. To further understand the mechanisms underlying PALB2-mediated DNA repair and tumor suppression functions, we targeted Palb2 in the mouse. Palb2-deficient murine ES cells recapitulated DNA damage defects caused by PALB2 depletion in human cells, and germ-line deletion of Palb2 led to early embryonic lethality. Somatic deletion of Palb2 driven by K14-Cre led to mammary tumor formation with long latency. Codeletion of both Palb2 and Tumor protein 53 (Trp53) accelerated mammary tumor formation. Like BRCA1 and BRCA2 mutant breast cancers, these tumors were defective in RAD51 focus formation, reflecting a defect in Palb2 HR-DSBR function, a strongly suspected contributor to Brca1, Brca2, and Palb2 mammary tumor development. However, unlike the case of Brca1-mutant cells, Trp53bp1 deletion failed to rescue the genomic instability of Palb2- or Brca2-mutant primary lymphocytes. Therefore, Palb2-driven DNA damage control is, in part, distinct from that executed by Brca1 and more similar to that of Brca2. The mechanisms underlying Palb2 mammary tumor suppression functions can now be explored genetically in vivo.     

Y-chromosomal STR haplotype analysis reveals surname-associated strata in the East-German population

In human populations, the correct historical interpretation of a genetic structure is often hampered by an almost inherent inability to differentiate between ancient and more recent influences upon extant gene pools. One method to trace recent population movements is the analysis of surnames, which, at least in Central Europe, can be thought of as traits 'linked' to the Y chromosome. Illegitimacy, extramarital birth and changes of surnames may have substantially obscured this linkage. In order to assess the actual extent of correlation between surnames and Y-chromosomal haplotypes in Central Europe, we typed Y-chromosomal short tandem repeat markers in 419 German males from Halle. These individuals were subdivided into three groups according to the origin of their respective surname, namely German (G), Slavic (S) or 'Mixed' (M). The distribution of the haplotypes was compared by Analysis of Molecular Variance. While the M group was indistinguishable from group G (PhiST=-0.0008, P>0.5), a highly significant difference (PhiST=0.0277, P<0.001) was observed between the S group and the combined G+M group. This surprisingly strong differentiation is comparable to that of European populations of much larger geographic and linguistic difference. In view of the major migration from Slavic countries into Germany in the 19th century, it appears likely that the observed concurrence of Slavic surnames and Y chromosomes is of a recent rather than an early origin. Our results suggest that surnames may provide a simple means to stratify, and thereby to render more efficient, Y-chromosomal analyses of Central Europeans that target more ancient events.     

The ALK(F1174L) mutation potentiates the oncogenic activity of MYCN in neuroblastoma

The ALK(F1174L) mutation is associated with intrinsic and acquired resistance to crizotinib and cosegregates with MYCN in neuroblastoma. In this study, we generated a mouse model overexpressing ALK(F1174L) in the neural crest. Compared to ALK(F1174L) and MYCN alone, co-expression of these two oncogenes led to the development of neuroblastomas with earlier onset, higher penetrance, and enhanced lethality. ALK(F1174L)/MYCN tumors exhibited increased MYCN dosage due to ALK(F1174L)-induced activation of the PI3K/AKT/mTOR and MAPK pathways, coupled with suppression of MYCN pro-apoptotic effects. Combined treatment with the ATP-competitive mTOR inhibitor Torin2 overcame the resistance of ALK(F1174L)/MYCN tumors to crizotinib. Our findings demonstrate a pathogenic role for ALK(F1174L) in neuroblastomas overexpressing MYCN and suggest a strategy for improving targeted therapy for ALK-positive neuroblastoma.     

BAFF-R, the major B cell-activating factor receptor, is expressed on most mature B cells and B-cell lymphoproliferative disorders

B cell-activating factor receptor (BAFF-R) is one of three known receptors for BAFF, a critical regulator of B- and T-cell function. In mice, BAFF-R is required for B-cell maturation and survival, and in mice and humans, the overproduction of BAFF is associated with autoimmune disease. We sought to determine the normal pattern of BAFF-R expression at specific stages of B- and T-cell development and whether this pattern of expression corresponds with related B- and T-cell neoplasms. Most circulating human B cells and a small subset of T cells are BAFF-R-positive. In reactive lymphoid tissues, BAFF-R is expressed by B cells colonizing the mantle zones, by a subset of cells within germinal centers, and rare cells in the interfollicular T-cell zone. BAFF-R is also expressed by B cells colonizing the splenic marginal zone. Seventy-seven (78%) of 116 cases of B-cell lymphoproliferative disorders were BAFF-R-positive by immunohistochemical and/or flow cytometric immunophenotypic analysis, including most cases of mantle cell lymphoma, follicular lymphoma, marginal zone lymphoma, chronic lymphocytic leukemia, hairy cell leukemia, and diffuse large B-cell lymphoma. In contrast, cases of precursor B lymphoblastic lymphoma, Burkitt lymphoma, and nodular lymphocyte-predominant Hodgkin lymphoma exhibit weak to negative staining for BAFF-R. All cases of classical Hodgkin lymphoma and T-cell lymphomas were BAFF-R-negative, including all cases of anaplastic large cell lymphoma, adult T-cell leukemia/lymphoma, angioimmunoblastic T-cell lymphoma, and peripheral T-cell lymphoma, unspecified. These findings highlight BAFF-R as a marker of both normal and neoplastic B cells and raise the possibility that BAFF-R expression is necessary for the survival of a subset of neoplastic B lymphocytes analogous to its known role in promoting normal B-cell maturation and survival.     

The CD45 isoform B220 identifies select subsets of human B cells and B-cell lymphoproliferative disorders

The B220 isoform of CD45, a pan B-cell marker in mice, is expressed by only a subset of human B cells that do not express the memory B-cell marker CD27, suggesting that it is a differentiation-specific isoform of CD45. We examined normal human peripheral blood B cells, secondary lymphoid tissue, and a range of human B-cell lymphoproliferative disorders for the expression of B220 by flow cytometric immunophenotyping and immunohistochemical staining. We found that a subset of human B cells in peripheral blood is positive for B220 by flow cytometric immunophenotypic analysis. In reactive lymphoid tissues, B220 is expressed by B cells occupying the mantle zones and by a subpopulation of germinal center cells, but, in contrast, marginal zone B cells in the spleen do not express B220. Of 94 cases of B-cell lymphoproliferative disorders, 33 (35%) were positive for B220 by flow cytometric immunophenotypic analysis, including most cases of marginal zone lymphoma, follicular lymphoma, and lymphoplasmacytic lymphoma. In contrast, all cases of precursor B lymphoblastic leukemia/lymphoma, mantle cell lymphoma, and chronic lymphocytic leukemia/small lymphocytic lymphoma were negative for B220. Immunohistochemical staining for B220 correlated with flow cytometric analysis for all cases studied by both methods. Our data demonstrate that B220 is expressed in a select subset of normal, reactive B cells in a pattern that is consistent with a marker of naive B cells. However, this restricted expression pattern is not seen in B-cell lymphoproliferative disorders. Discordance between the B220 expression patterns of normal mantle and marginal zone B cells and their respective neoplastic counterparts may aid in the distinction between normal and neoplastic proliferations at these anatomical sites.     

Selective CDK4/6 inhibition with tumor responses by PD0332991 in patients with mantle cell lymphoma

Mantle cell lymphoma (MCL) carries an unfavorable prognosis and requires new treatment strategies. The associated t(11:14) translocation results in enhanced cyclin D1 expression and cyclin D1-dependent kinase activity to promote cell-cycle progression. A pharmacodynamic study of the selective CDK4/6 inhibitor PD0332991 was conducted in 17 patients with relapsed disease, using 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) and 3-deoxy-3[(18)F]fluorothymidine (FLT) positron emission tomography (PET) to study tumor metabolism and proliferation, respectively, in concert with pre- and on-treatment lymph node biopsies to assess retinoblastoma protein (Rb) phosphorylation and markers of proliferation and apoptosis. Substantial reductions in the summed FLT-PET maximal standard uptake value (SUV(max)), as well as in Rb phosphorylation and Ki-67 expression, occurred after 3 weeks in most patients, with significant correlations among these end points. Five patients achieved progression-free survival time of > 1 year (range, 14.9-30.1+ months), with 1 complete and 2 partial responses (18% objective response rate; 90% confidence interval, 5%-40%). These patients demonstrated > 70%, > 90%, and ≥ 87.5% reductions in summed FLT SUV(max) and expression of phospho-Rb and Ki67, respectively, parameters necessary but not sufficient for long-term disease control. The results of the present study confirm CDK4/6 inhibition by PD0332991 at a well-tolerated dose and schedule and suggest clinical benefit in a subset of MCL patients. This study is registered at www.clinicaltrials.gov under identifier NCT00420056.     

Distribution of estrone sulfatase in rat brain determined by in vitro autoradiography with 16α-[F]fluoroestradiol-3,17β-disulfamate

16α-Fluoroestradiol-3,17β-disulfamate (FESDS) strongly inhibits estrone sulfatase (ES), an enzyme which is also present in the brain. The enzyme is probably involved in important regulatory functions of neurosteroids which may be disturbed in certain brain diseases. In the present study, [¹⁸F]FESDS was used to measure the amount of ES in various rat brain regions using quantitative in vitro autoradiography. The obtained values vary between 0.29 pmol (mg protein)^–1 (pons) and 11.5 pmol (mg protein)^–1 (striatum). They are positively correlated with the enzyme activity measured in homogenates of the corresponding regions. Because this radiotracer binds also to carbonic anhydrase in the brain it is only of limited use for in vivo imaging studies.