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

描述(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，而这些通路的异常激活推动表皮肿瘤的发生。MEK和JNK在大多数自发性人表皮鳞状细胞癌中被激活，但每种蛋白的两种亚型在角质形成细胞中表达，这些通路元件在人表皮中的明确功能尚未确定。MEK1基因缺失的小鼠是胚胎致死的，排除了表皮表型的建立；然而，MEK2基因缺失的小鼠是正常的。这表明MEK1与MEK2要么在功能上占优势，要么在功能上冗余。促进增殖和减少分化的表皮RAS效应仅被MEK1概括，提示MEK1起主要作用。然而，MEK1/2有很高的同源性，并且MEK2可以在多大程度上补偿MEK1的丢失尚不清楚。为了阐明MEK1/2在人类表皮动态平衡以及表皮肿瘤发生中的相关功能，我们将使用互补的RNAi和药理学方法来抑制人类表皮中的MEK1和MEK2。然后将确定MEK1/2支持RAS驱动的人类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缺失的小鼠表皮为发育不良，而JNK2缺失的表皮为过度增殖。然而，较薄的发育不良的JNK1缺失组织比野生型皮肤更容易形成肿瘤，而过度增殖的JNK2缺失组织则对肿瘤的形成具有抵抗力。JNK1/2在正常人表皮中的作用将通过RNAi、显性负性和药物抑制来确定。然后将确定JNK1/2与RAS协同作用在促进人表皮肿瘤形成中的必要性和充分性。AIMS I和II的基础假设是MEK1/2和JNK1/2在RAS驱动的表皮肿瘤发生中需要支持关键成分。在拟议的资助期结束时，我们希望明确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，作为未来治疗包括癌症在内的人类表皮生长和分化疾病的基础。

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.