CYCLOOXYGENASE AND PGE2 RECEPTOR FUNCTION IN SKIN CANCER

众所周知，紫外线照射是一种完全致癌物质，可诱导和促进皮肤基底细胞癌和鳞状细胞癌。最近的研究表明，环氧化酶产物前列腺素B2（PGE2）在鳞状细胞癌的发生和促进中起着重要作用。在该实验室最近的研究中，通过使用选择性环氧合酶-2 （COX-2）抑制剂塞来昔布治疗SKH无毛小鼠，紫外线诱导的肿瘤形成减少了近60%。这种保护作用也可能发生在人类身上。P6~与特定的细胞受体相互作用，调节细胞功能。随着最近四种不同的PGE2受体的克隆，现在有可能剖析前列腺素受体信号传导可能增强紫外线肿瘤发生的一些机制。我们的初步研究表明，原代人角质形成细胞大量表达前列腺素E2 （PGE2）的生长调节受体（EP2）和生长抑制受体（EP3）。我们的数据表明，高浓度的PGE2通过激活低亲和力的EP2受体偶联产生cAMP来刺激增殖，而增殖抑制是由高亲和力的EP3受体介导的，而EP3受体在低浓度的PGE2下具有活性。与该受体相关的信号通路定义不清，产生驱动其激活的PGE2数量的条件也不清楚。我们的初步数据表明，将EP3受体转染到HaCaT细胞中导致增殖降低。相比之下，EP2基因转染的hacat的增殖率增加。将EP2反义转染到HaCats中可以逆转这一情况。我们假设在基础条件下，PGE2信号主要通过与COX-1活性相关的高亲和力EP3受体发生，而炎症通过与COX-2相关的低亲和力EP2受体诱导信号传导。我们还假设，紫外线诱导的COX-2上调会增加组织中PGE2的水平，从而推动ep2介导的受照射细胞增殖。选择性COX-2抑制导致通过cox - 1产生低nM浓度的PGE2，允许选择性刺激高亲和力EP3受体介导增强分化。通过广泛表征基础和紫外线对EP受体信号传导的影响，本研究将更好地定义紫外线诱导的PGE2形成、环加氧酶活性和EP受体信号传导之间的关系。EP受体对角质细胞增殖、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.