Physiologic Function of RAS Effectors MEK 1/2 on Epidermal Differentiation

描述（由申请人提供）：通过Ras/Raf/MEK/ERK和平行的MEKK/JNKK2/JNK MAP激酶级联的生理信号调节正常的表皮稳态，而这些途径的异常激活驱动表皮瘤变。MEK和JNK在大多数自发性人表皮鳞状细胞癌中被激活，然而，每种蛋白的两个亚型在角质形成细胞中表达，并且这些通路元件在人表皮中的明确功能作用尚未确定。MEK1缺失小鼠是胚胎致死性的，阻止了表皮表型的建立；然而，MEK2缺失小鼠是正常的。这表明MEK1在功能上占主导地位，或者与MEK2在功能上冗余。表皮Ras对增殖增加和分化减少的影响仅由MEK1再现，表明MEK1起主要作用。然而，MEK1/2具有高度同源性，MEK2在多大程度上弥补MEK1的损失尚不清楚。为了阐明MEK1/2在人表皮稳态以及表皮肿瘤发生中的相对功能作用，我们将采用互补的RNAi和药理学方法来抑制人表皮中的MEK1和MEK2。然后将定义MEK1/2支持Ras驱动的人表皮肿瘤发生的必要性和充分性。JNK1和JNK2在表皮中似乎具有相反的作用。JNK1缺失的小鼠表皮是发育不全的，而JNK2缺失的小鼠表皮是增生性的。然而，较薄的发育不全的JNK1无组织比野生型皮肤更容易形成肿瘤，而高增殖的JNK2无组织则对肿瘤发生具有抗性。JNK1/2在正常人表皮中的作用将通过RNAi、显性阴性和药物抑制来确定。进而确定JNK1/2与Ras协同驱动人表皮肿瘤形成的必要性和充分性。目的I和II基于这样的假设：MEK1/2和JNK1/2是支持Ras驱动的表皮肿瘤发生的关键成分所必需的。在拟议的资助期完成后，我们希望确定MEK1/2和JNK1/2信号在正常人类表皮稳态和ras驱动的肿瘤发生中的重要性，作为未来治疗人类表皮生长和分化障碍（包括癌症）的基础。

DESCRIPTION (provided by applicant): Physiologic signaling through the Ras/Raf/MEK/ERK and parallel MEKK/JNKK2/JNK MAP kinase cascades regulates normal epidermal homeostasis, while aberrant activation of these pathways drives epidermal neoplasia. MEK and JNK are activated in a majority of spontaneous human epidermal squamous cell carcinomas, however, two isoforms of each protein are expressed in keratinocytes, and clear functional roles for these pathway elements in human epidermis have not been established. MEK1 null mice are embryonic lethal, precluding establishment of epidermal phenotypes; however, MEK2 null mice are normal. This suggests that MEK1 is either functionally dominant, or functionally redundant with MEK2. The epidermal Ras effects of increased proliferation and decreased differentiation are recapitulated only by MEK1, suggesting a primary role for MEK1. However, MEK1/2 share high homology, and the extent to which MEK2 can compensate for MEK1 loss is unknown. To clarify the relative functional roles of MEK1/2 in human epidermal homeostasis, as well as in epidermal tumorigenesis, we will use complementary RNAi and pharmacologic approaches to inhibit MEK1 and MEK2 in human epidermis. The necessity and sufficiency of MEK1/2 to support Ras driven human epidermal tumorigenesis will then be defined. JNK1 and JNK2 appear to have opposing effects in epidermis. Murine epidermis null for JNK1 is hypoplastic, while JNK2 null epidermis is hyperproliferative. However, the thin hypoplastic JNK1 null tissue is more susceptible than wild type skin to tumor formation, while the hyperproliferative JNK2 null tissue is resistant to tumorigenesis. JNK1/2 roles in normal human epidermis will be defined through RNAi, dominant negative and pharmacologic inhibition. The necessity and sufficiency of JNK1/2 to cooperate with Ras in driving human epidermal tumor formation will then be determined. Aims I and II are based on the hypothesis that MEK1/2 and JNK1/2 are required to support key components of Ras driven epidermal tumorigenesis. At the completion on the proposed funding period, we hope to have defined the importance of MEK1/2 and JNK1/2 signaling in both normal human epidermal homeostasis, and in Ras-driven tumorigenesis as a basis for future therapeutic efforts for human disorders of epidermal growth and differentiation, including cancer.