CYCLOOXYGENASE AND PGE2 RECEPTOR FUNCTION IN SKIN CANCER

紫外线暴露是已知的一个完整的致癌物质诱导和促进皮肤的基底细胞和鳞状细胞癌。最近的研究表明，环氧合酶产物前列腺素B2（PGE 2）对鳞状细胞癌的发生和促进有重要作用。在该实验室最近的研究中，通过使用选择性环氧合酶-2（考克斯-2）抑制剂塞来昔布治疗SKH无毛小鼠，UV诱导的肿瘤形成减少了近60%。这种保护也可能发生在人类身上。P6~+与特异性细胞受体相互作用以调节细胞功能。随着最近四种不同的前列腺素E2受体的克隆，现在有可能剖析前列腺素受体信号传导可能起作用以增强UV肿瘤发生的一些机制。我们的初步工作表明，原代人角质形成细胞表达前列腺素E2（PGE 2）的生长调节（EP 2）和生长抑制（EP 3）受体。我们的数据显示，高浓度的PGE 2通过激活与cAMP产生偶联的低亲和力EP 2受体来刺激增殖，而增殖的抑制是由高亲和力EP 3受体介导的，所述EP 3受体在低10倍的PGE 2浓度下具有活性。与这种受体相关的信号通路定义不清，产生大量PGE 2的条件也是如此，PGE 2驱动其激活。我们的初步数据表明，EP 3受体转染到HaCaT细胞的结果在减少增殖。相反，EP 2正义转染的HaCaTs具有增加的增殖率。将EP 2反义转染到HaCats中逆转了这一情况。我们假设在基础条件下，PGE 2信号主要通过与考克斯-1活性相关的高亲和力EP 3受体发生，而炎症通过与考克斯-2相关的低亲和力EP 2受体诱导信号。我们还假设UV诱导的考克斯-2上调增加组织中的PGE 2水平，从而驱动照射细胞中EP 2介导的增殖。选择性考克斯-2抑制，导致通过COX-1产生的低nM浓度的PGE 2，允许选择性刺激介导增强分化的高亲和力EP 3受体。提出的工作将更好地定义紫外线诱导的PGE 2形成，环氧合酶活性，EP受体信号之间的关系，通过广泛的基础和紫外线对EP受体信号的影响。EP受体对角质形成细胞增殖、凋亡和分化的影响将作为皮肤肿瘤的标志物进行研究。

Ultraviolet light exposure is known to be a complete carcinogen inducing & promoting basal cell and squamous cell carcinoma of the skin. Recent work has shown that significant contributions to squamous cell carcinoma initiation and promotion are made by the cyclooxygenase product prostaglandin B2(PGE2). In recent studies from this lab, UV-induced tumor formation was decreased nearly 60% by treatment of SKH hairless mice with the selective cyclooxygenase-2 (COX-2) inhibitor celecoxib. This protection may also occur in humans. P6~ interacts with specific cellular receptors to regulate cell function. With the recent cloning of four different PGE2 receptors, it is now possible to dissect some of the mechanisms by which prostaglandin receptor signaling may act to enhance UV tumorigenesis. Our preliminary work demonstrates that primary human keratinocytes express both growth-stipulatory (EP2) and growth- inhibitory (EP3) receptors for prostaglandin E2 (PGE2) in significant amounts. Our data shows that high concentrations of PGE2 stimulate proliferation by activating low-affinity EP2 receptors coupled to production of cAMP, while inhibition of proliferation is mediated by high- affinity EP3 receptors which are active at 10-fold lower concentrations of PGE2. The signaling pathways linked to this receptor are poorly defined, as are the conditions for generating quantities of PGE2 which drive its activation. Our preliminary data have shown that transfection of the EP3 receptor into HaCaT cells results in decreased proliferation. In contrast, EP2 sense transfected HaCaTs have increased proliferative rates. EP2 antisense transfection into HaCats reverses this picture. We hypothesize that under basal conditions, PGE2 signaling occurs primarily through the high affinity EP3 receptor linked to COX-1 activity, while inflammation induces signaling via the low affinity EP2 receptor linked to COX-2.We also hypothesize that UV-induced upregulation of COX-2 increases tissue PGE2 levels, driving EP2-mediated proliferation in irradiated cells. Selective COX-2 inhibition, resulting in low nM concentrations of PGE2 produced via COX-l, permits selective stimulation of high affinity EP3 receptors mediating enhanced differentiation. The work proposed will better define the relationship between UV-induced PGE2 formation, cyclooxygenase activity, and EP receptor signaling through extensive characterization of basal and UV effects on EP receptor signaling. EP receptor effects on keratinocyte proliferation, apoptosis and differentiation will be studied as markers of cutaneous neoplasia.