黑素细胞对表皮渗透屏障功能的影响

表皮渗透屏障功能是表皮的主要生理功能之一,深肤色个体较浅肤色个体具有更优越的表皮屏障功能,提示黑素细胞和/或黑素与表皮渗透屏障功能密切相关.有关黑素细胞对角质形成细胞及对表皮渗透屏障功能影响的机制尚不清楚,近几年研究发现,酸性黑素小体进入表皮可能是深肤色者表皮屏障功能增强的细胞基础,表皮pH对增强屏障功能重要性不可忽视,内源性酸化机理可能提供一个促进深肤色个体表皮酸化的新机制.此外,黑素细胞-角质形成细胞的交叉对话及相关信号机制可能在增强表皮渗透屏障功能中起重要作用.     

Toll样受体4的活化抑制人表皮原代黑素细胞的黑素合成

目的探讨黑素细胞Toll样受体4(TLR4)的活化对黑素细胞黑素合成的影响。方法以原代培养的黑素细胞为研究对象,采用TLR4的激动剂脂多糖(LPS)刺激细胞,首先检测黑素含量的变化,其次用实时定量PCR和Western blot法检测前黑素体蛋白(Pmel17)、酪氨酸酶(TYR)、小眼畸形相关转录因子(MITF)的表达变化;最后用电镜观察黑素小体的变化。结果 LPS刺激细胞后,黑素含量明显减少,黑素合成相关蛋白Pmel17和TYR的表达降低,且这种变化依赖于MITF转录因子的调控,同时电镜结果显示黑素小体合成被抑制。结论 TLR4的活化降低黑素细胞的黑素合成,提示细菌的产物可以通过天然免疫影响黑素合成。     

UVA及UVB诱导人皮肤光生物学反应差异的研究进展

紫外线刺激皮肤后,表皮黑素细胞通过合成黑素,转移至临近的角质形成细胞,对皮肤起光保护作用.皮肤遭受过量紫外线刺激后出现一系列损伤反应,包括晒黑及炎症反应、细胞DNA损伤、光致癌作用等,UVA及UVB因波长不同,照射皮肤后出现的生物学反应存在差异.目前有关UVA及UVB刺激表皮细胞后的损伤反应机制一直是研究热点,研究两种紫外线所引起的光损伤机制之间的差异有益于预防一系列光损伤性疾病.     

α-促黑素对全肾缺血再灌注模型大鼠的作用（英文）

背景:肾脏缺血再灌注常合并肾脏及肺脏的急性损伤,且角质细胞生长因子受体及钠通道蛋白在缺血再灌注致急性肾、肺损伤中的表达变化及α-促黑素的治疗作用有待于进一步观察及研究。目的:探索全肾缺血再灌注模型大鼠中角质细胞生长因子受体、钠通道蛋白的表达以及α-促黑素的治疗作用。方法:选择健康雄性SD大鼠30只按随机数字表法等分为对照组、缺血再灌注造模组和α-促黑素干预组。缺血再灌注造模组和α-促黑素组大鼠通过肾动脉结扎30 min建立全肾缺血/再灌注模型,对照组大鼠仅暴露肾动脉不结扎。α-促黑素干预组大鼠于造模前30 min腹腔注射α-促黑素(0.25 mg/kg)进行干预,缺血再灌注造模组大鼠注射等量(4 mL)生理盐水。结果与结论:与对照组相比,缺血再灌注造模组与α-促黑素干预组大鼠肾、肺组织含水量明显升高,角质细胞生长因子受体、钠通道蛋白的表达明显下降(P0.05);与缺血再灌注造模组相比,α-促黑素干预组大鼠肾、肺组织含水量明显减少,而角质细胞生长因子受体、钠通道蛋白mR NA及蛋白的表达明显升高(P0.05),且大鼠肾、肺组织充血水肿明显减轻。提示肾缺血再灌注后,角质细胞生长因子受体、钠通道蛋白的表达变化与肾、肺充血水肿等损伤一致,而α-促黑素可以增加角质细胞生长因子受体、钠通道蛋白的表达水平,减轻肾及肺组织的损伤,发挥一定的保护作用。     

P53 抑制剂和微管抑制剂对银屑病表皮角质形成细胞糖皮质激素受体核转运的影响

目的:探讨P53抑制剂和微管抑制剂对银屑病表皮角质形成细胞糖皮质激素受体(GR)核转运的影响。方法:分离和培养银屑病患者和正常人表皮角质形成细胞,分别与P53抑制剂和微管蛋白抑制剂共培养,加或不加血管内皮细胞生长因子(VEGF),间接免疫荧光法检测上述因素对GR核转位的影响。结果:VEGF可诱导正常角质形成细胞发生核转位;P53抑制剂抑制了VEGF诱导的GR核转位。与VEGF共培养的角质形成细胞的核转位评分显著低于单纯角质形成细胞的核转运评分,差异有统计学意义(P0.05);微管抑制剂可完全将正常表皮角质形成细胞的GR滞留在胞浆中,在加入VEGF后,与单纯微管抑制剂组比较,胞浆中GR并没有明显增多;而微管抑制剂和P53抑制剂共培养,会有少量GR进入角质形成细胞的胞核中。结论:微管介导银屑病角质形成细胞GR的核摄取,P53参与了GR的核输出。     

α-促黑素对全肾缺血再灌注模型大鼠的作用

背景：肾脏缺血再灌注常合并肾脏及肺脏的急性损伤,且角质细胞生长因子受体及钠通道蛋白在缺血再灌注致急性肾、肺损伤中的表达变化及α-促黑素的治疗作用有待于进一步观察及研究。 目的：探索全肾缺血再灌注模型大鼠中角质细胞生长因子受体、钠通道蛋白的表达以及α-促黑素的治疗作用。 方法：选择健康雄性SD大鼠30只按随机数字表法等分为对照组、缺血再灌注造模组和α-促黑素干预组。缺血再灌注造模组和α-促黑素组大鼠通过肾动脉结扎  30 min 建立全肾缺血/再灌注模型,对照组大鼠仅暴露肾动脉不结扎。α-促黑素干预组大鼠于造模前30 min腹腔注射α-促黑素(0.25 mg/kg)进行干预,缺血再灌注造模组大鼠注射等量(4 mL)生理盐水。 结果与结论：与对照组相比,缺血再灌注造模组与α-促黑素干预组大鼠肾、肺组织含水量明显升高,角质细胞生长因子受体、钠通道蛋白的表达明显下降(P < 0.05);与缺血再灌注造模组相比,α-促黑素干预组大鼠肾、肺组织含水量明显减少,而角质细胞生长因子受体、钠通道蛋白mRNA及蛋白的表达明显升高(P < 0.05),且大鼠肾、肺组织充血水肿明显减轻。提示肾缺血再灌注后,角质细胞生长因子受体、钠通道蛋白的表达变化与肾、肺充血水肿等损伤一致,而α-促黑素可以增加角质细胞生长因子受体、钠通道蛋白的表达水平,减轻肾及肺组织的损伤,发挥一定的保护作用。 中国组织工程研究杂志出版内容重点：肾移植;肝移植;移植;心脏移植;组织移植;皮肤移植;皮瓣移植;血管移植;器官移植;组织工程     

皮肤黑素的代谢及其影响因素

人类皮肤颜色的各种差异与黑素细胞中黑素小体的数目、大小、类型和分布有着直接的关系.黑素的合成及其在细胞内的转运是非常复杂而精确的过程,该过程决定皮肤色素的分布与沉着.有诸多因素影响着黑素的代谢,目前研究较多的有酪氨酸酶、过氧化物酶、微量元素、紫外线、结构蛋白Pmel 17和蛋白受体2等.     

Rho GTP酶对肌动蛋白细胞骨架的作用

在所有真核细胞中 ,肌动蛋白细胞骨架介导了许多必需的生物学功能。除提供确定细胞形状和极性所必需的结构框架外 ,肌动蛋白细胞骨架尤其是其动力学变化还与细胞的运动、分裂、粘附以及吞噬等过程密切相关。RhoGTP酶家族是一类参与众多细胞信号转导通路的重要蛋白 ,其家组成员是联系膜表面受体与肌动蛋白细胞骨架的关键调节分子 ,起着分子开关的作用。反应于细胞外信号它们诱导肌动蛋白细胞骨架组织的相应改变 ,以引发大量生物学反应包括 :形态形成、趋化作用及轴突的定向。     

异欧前胡素抑制人表皮黑素细胞c-Kit蛋白的表达

目的探索异欧前胡素对体外人表皮黑素细胞c-kit蛋白表达的作用。方法体外分离、纯化培养人表皮黑素细胞,随机分为1组(对照组)、2组(10 nmol/L SCF组)、3组(25μmol/L异欧前胡素组)和4组(25μmol/L异欧前胡素+10nmol/L SCF组),各组黑素细胞按设定条件培养48 h,倒置显微镜观察黑素细胞的形态,免疫荧光显微镜观察黑素细胞的干细胞因子受体c-Kit蛋白表达和分布,NaOH裂解法测定黑素细胞黑素的含量。结果与1组比较,2组黑素细胞胞体增大,3组黑素细胞胞体变小,树状突起变长,4组黑素细胞胞体小于2组。免疫荧光显微镜观察可见1组黑素细胞c-kit蛋白表达呈红色荧光,分布于胞膜,2组黑素细胞c-Kit蛋白由于SCF诱导而表达增强,3组、4组黑素细胞c-Kit蛋白因异欧前胡素的抑制而表达减弱,各组黑素细胞c-Kit蛋白表达的结果与1组比较,差异有统计学意义(P0.01)。黑素含量检测结果表明,异欧前胡素对SCF诱导的黑素细胞黑素的合成有抑制作用,2组、3组、4组与1组之间黑素含量的差异、4组与2组之间黑素含量的差异均具有统计学意义(P0.05,P0.01)。结论 25μmol/L异欧前胡素可抑制体外培养人表皮黑素细胞c-Kit蛋白的表达,调节SCF/c-Kit信号传导而降低黑素细胞的黑素含量。     

过氧化氢对白癜风患者黑素细胞的氧化损伤

目的探讨过氧化氢(H2O2)对体外培养黑素细胞的影响及氧化应激与白癜风发病的关系。方法培养的黑素细胞中加入H2O2,用MTT法检测黑素细胞增殖,NaOH法检测黑素合成。结果H2O2可以抑制黑素细胞增殖及黑素合成,且具有浓度和时间依赖性。结论氧化应激可以抑制黑素细胞增殖及黑素合成,提示氧化损伤不足以诱发白癜风皮损。     

RhoA activation promotes transendothelial migration of monocytes via ROCK

Monocyte infiltration into inflamed tissue requires the initial arrest of the cells on the endothelium followed by firm adhesion and their subsequent migration. Migration of monocytes and other leukocytes is believed to involve a coordinated remodeling of the actin cytoskeleton. The small GTPases RhoA, Rac1, and Cdc42 are critical regulators of actin reorganization. In this study, we have investigated the role of Rho-like GTPases RhoA, Rac1, and Cdc42 in the adhesion and migration of monocytes across brain endothelial cells by expressing their constitutively active or dominant-negative constructs in NR8383 rat monocytic cells. Monocytes expressing the active form of Cdc42 show a reduced migration, whereas Rac1 expression did not affect adhesion or migration. In contrast, expression of the active form of RhoA in monocytes leads to a dramatic increase in their adhesion and migration across endothelial cells. The effect of RhoA was found to be mediated by its down-stream effector Rho kinase (ROCK), as pretreatment with the selective ROCK inhibitor Y-27632 prevented this enhanced adhesion and migration. These results demonstrate that RhoA activation in monocytes is sufficient to enhance adhesion and migration across monolayers of endothelial cells.     

Cdc42 and the actin-related protein/neural Wiskott-Aldrich syndrome protein network mediate cellular invasion by Cryptosporidium parvum

Cryptosporidium parvum invasion of epithelial cells involves host cell membrane alterations which require a remodeling of the host cell actin cytoskeleton. In addition, an actin plaque, possibly associated with the dense-band region, forms within the host cytoplasm at the host-parasite interface. Here we show that Cdc42 and RhoA, but not Rac1, members of the Rho family of GTPases, are recruited to the host-parasite interface in an in vitro model of human biliary cryptosporidiosis. Interestingly, activation of Cdc42, but not RhoA, was detected in the infected cells. Neural Wiskott-Aldrich syndrome protein (N-WASP) and p34-Arc, actin-regulating downstream effectors of Cdc42, were also recruited to the host-parasite interface. Whereas cellular expression of a constitutively active mutant of Cdc42 promoted C. parvum invasion, overexpression of a dominant negative mutant of Cdc42, or depletion of Cdc42 mRNA by short interfering RNA-mediated gene silencing, inhibited C. parvum invasion. Expression of the WA fragment of N-WASP to block associated actin polymerization also inhibited C. parvum invasion. Moreover, inhibition of host cell Cdc42 activation by dominant negative mutation inhibited C. parvum-associated actin remodeling, membrane protrusion, and dense-band formation. In contrast, treatment of cells with a Rho inhibitor, exoenzyme C3, or cellular overexpression of dominant negative mutants of RhoA and Rac1 had no effect on C. parvum invasion. These data suggest that C. parvum invasion of target epithelia results from the organism's ability to activate a host cell Cdc42 GTPase signaling pathway to induce host cell actin remodeling at the attachment site.     

Involvement of Rho and Rac small G proteins and Rho GDI in Ca2+-dependent exocytosis from PC12 cells

Background : The Rho small G protein family, which includes the Rho, Rac and Cdc42 subfamilies, is implicated in various cell functions such as cell shape change, cell motility and cytokinesis, through the reorganization of actin filaments. Rho GDI is an inhibitory regulator of the Rho small G protein family and inhibits the Rho family dependent cell functions. Reorganization of actin filaments is also known to regulate Ca²⁺-dependent exocytosis.
Results: We have examined here whether the Rho family members are also involved in Ca²⁺-dependent exocytosis. We have found, by the use of the human growth hormone (GH) co-expression assay system on PC12 cells, that overexpression of Rho GDI inhibits high K⁺-induced, Ca²⁺-dependent GH release. This inhibitory action of Rho GDI is restored by co-expression of a dominant active mutant of RhoA or Rac1, but not of a dominant active mutant of Cdc42. C3 transferase, known to ADP-ribosylate Rho and to inhibit its function, also inhibits this GH release. Overexpression of a dominant active mutant of RhoA or Rac1 alone shows only a small effect on GH release. Moreover, immunocytochemical studies show that the overexpression of Rho GDI prevents a partial disruption of the cortical actin network which accompanies exocytosis.
Conclusions: These results suggest that RhoA, Rac1 and Rho GDI are involved in Ca²⁺-dependent exocytosis at least partly through the reorganization of actin filaments, and that the activation of RhoA or Rac1 alone is not sufficient for this reaction.     

Pseudomonas aeruginosa ExoT is a Rho GTPase-activating protein

Transient intracellular expression of ExoT in CHO cells stimulated cell rounding and actin reorganization. Biochemical studies showed that ExoT was a GTPase-activating protein for RhoA, Rac1, and Cdc42. Together, these data show that ExoT interferes with Rho signal transduction pathways, which regulate actin organization, exocytosis, cell cycle progression, and phagocytosis.     

Cytosolic delivery and characterization of the TcdB glucosylating domain by using a heterologous protein fusion

TcdB from Clostridium difficile glucosylates small GTPases (Rho, Rac, and Cdc42) and is an important virulence factor in the human disease pseudomembranous colitis. In these experiments, in-frame genetic fusions between the genes for the 255 amino-terminal residues of anthrax toxin lethal factor (LFn) and the TcdB(1-556) coding region were constructed, expressed, and purified from Escherichia coli. LFnTcdB(1-556) was enzymatically active and glucosylated recombinant RhoA, Rac, Cdc42, and substrates from cell extracts. LFnTcdB(1-556) plus anthrax toxin protective antigen intoxicated cultured mammalian cells and caused actin reorganization and mouse lethality, all similar to those caused by wild-type TcdB.     

Role of the Rho GTPase-activating protein RICS in neurite outgrowth

The Rho family of small GTPases, including RhoA, Rac1 and Cdc42, are critical regulators of the actin cytoskeleton. In neuronal systems, Rho GTPase-activating proteins (RhoGAPs) and their substrates, Rho GTPases, have been implicated in regulating multiple processes in the morphological development of neurons, including axonal growth and guidance, dendritic elaboration and formation of synapses. RICS is mainly expressed in the brain and functions as a RhoGAP protein for Cdc42 and Rac1 in vitro. To examine the biological function of RICS, we disrupted the RICS gene in mice. RICS knockout mice developed normally and were fertile. However, when cultured in vitro, Cdc42 activity in RICS(-/-) neurons was higher than that in wild-type neurons. Consistent with this finding, hippocampal and cerebellar granule neurons derived from RICS(-/-) mice bore longer neurites than those from wild-type mice. These findings suggest that RICS plays an important role in neurite extension by regulating Cdc42 in vivo.     

Bacterial protein toxins inhibiting low-molecular-mass GTP-binding proteins

The Rho GTPases, which belong to the Ras superfamily of low-molecular-mass GTP-binding proteins, are the preferred intracellular targets of bacterial protein toxins. The Rho GTPases RhoA/B/C, Rac1/2 and Cdc42 are the master regulators of the actin cytoskeleton. Clostridium difficile toxins A and B, the causative agents of the antibiotic-associated pseudomembranous colitis, are intracellularly acting cytotoxins which mono-glucosylate the Rho GTPases. Clostridium botulinum C3 toxin, which is not related to the clostridial neurotoxins, catalyses ADP-ribosylation of RhoA/B/C but not of other Rho GTPases. Glucosylation as well as ADP-ribosylation result in functional inactivation of Rho causing disassembly of the actin cytoskeleton.     

Difference in the cytotoxic effects of toxin B from Clostridium difficile strain VPI 10463 and toxin B from variant Clostridium difficile strain 1470

Glucosylation of RhoA, Rac1, and Cdc42 by Clostridium difficile toxin B from strain VPI 10463 (TcdB) results in actin reorganization (cytopathic effect) and apoptosis (cytotoxic effect). Toxin B from variant C. difficile strain 1470 serotype F (TcdBF) differs from TcdB with regard to substrate proteins, as it glucosylates Rac1 and R-Ras but not RhoA and Cdc42. In this study, we addressed the question of whether the cellular effects of the toxins depend on their protein substrate specificity. Rat basophilic leukemia (RBL) cells were synchronized using the thymidine double-block technique. We show that cells were most sensitive to the cytotoxic effect of TcdB in S phase, as analyzed in terms of phosphatidyl serine externalization, fragmentation of nuclei, and activation of caspase-3; in contrast, TcdBF induced only a marginal cytotoxic effect, suggesting that inactivation of RhoA (but not of Rac1) was required for the cytotoxic effect. The glucosylation of Rac1 was correlated to the cytopathic effect of either toxin, suggesting a close connection of the two effects. The cytotoxic effect of TcdB was executed by caspase-3, as it was responsive to inhibition by acetyl-Asp-Met-Gln-Asp-aldehyde (Ac-DMQD-CHO), an inhibitor of caspase-3. The viability of TcdB-treated RBL cells was reduced, whereas the viability of TcdBF-treated cells was unchanged, further confirming that inactivation of RhoA is required for the cytotoxic effect. In conclusion, the protein substrate specificity of the glucosylating toxins determines their biological activity.     

Calcium-dependent interaction of Lis1 with IQGAP1 and Cdc42 promotes neuronal motility

Lis1 gene defects impair neuronal migration, causing the severe human brain malformation lissencephaly. Although much is known about its interactions with microtubules, microtubule-binding proteins such as CLIP-170, and with the dynein motor complex, the response of Lis1 to neuronal motility signals has not been elucidated. Lis1 deficiency is associated with deregulation of the Rho-family GTPases Cdc42, Rac1 and RhoA, and ensuing actin cytoskeletal defects, but the link between Lis1 and Rho GTPases remains unclear. We report here that calcium influx enhances neuronal motility through Lis1-dependent regulation of Rho GTPases. Lis1 promotes Cdc42 activation through interaction with the calcium sensitive GTPase scaffolding protein IQGAP1, maintaining the perimembrane localization of IQGAP1 and CLIP170 and thereby tethering microtubule ends to the cortical actin cytoskeleton. Lis1 thus is a key component of neuronal motility signal transduction that regulates the cytoskeleton by complexing with IQGAP1, active Cdc42 and CLIP-170 upon calcium influx.     

Recombinant AexU effector protein of Aeromonas veronii bv. sobria disrupts the actin cytoskeleton by downregulation of Rac1 and induces direct cytotoxicity to β4-integrin expressing cell lines

AexU is a type three secretion system (TTSS) effector of Aeromonas hydrophila which has an in vitro ADP-ribosyltransferase (ART) and GTPase-activating protein (GAP) activities on Rac1, RhoA and Cdc42. Here we show that, AexU of Aeromonas veronii bv. sobria AeG1 strain disrupts actin cytoskeleton of HeLa cells during AeG1 infection, aexU transfection or direct application of AexU protein. Such cellular disruption was rescued by either inactivation of AexU-GAP activity by substitution of arginine residue 143 to alanine or expression of a constitutively active (CA) Rac1 but not CA RhoA or CA Cdc42. On the other hand, AexU was found co-localized with β4-integrin probably through its Arg-Gly-Asp (RGD) integrin binding motif (319–321) residues. Interestingly, direct application of GST-AexU-HA fusion protein caused significant cytotoxic effect on β4-integrin expressing HT-29 cells. In contrast, β4-integrin blockade with a specific antibody reduced such cytotoxicity. Consequently, AexU cytotoxic effect was exaggerated with a greater expression of β4-integrin in Caco-2 and HeLa cells, while it was incompetent on β4-integrin non-expressing CHO cells. As far as we know, this is a novel TTSS effector which specifically inactivates Rac1 to disrupt actin cytoskeleton and has an alternative cytotoxic pathway through β4-integrin mediation.