Neill Graham W, Ghali Lucy R, Green Judith L, Ikram Mohammed S, Philpott Michael P, Quinn Anthony G
Centre for Cutaneous Research, Barts and the London, Queen Mary's School of Medicine and Dentistry, University of London, 2 Newark Street, Whitechapel, London E1 2AT, United Kingdom.
Cancer Res. 2003 Aug 1;63(15):4692-7.
Activation of the Sonic hedgehog signaling pathway, primarily through mutational inactivation of the PTCH1 gene, is associated with the development of basal cell carcinoma (BCC). Gli1, a member of the Gli family of transcription factors, is expressed in BCC and in transgenic mice targeted expression of Gli1 in basal keratinocytes leads to BCC development. In addition to BCC, previous studies have shown that Gli1 is expressed in the outer root sheath (ORS) of the hair follicle but is absent in interfollicular epidermis. In this study, we have characterized the expression pattern of two protein kinase C (PKC) isoforms expressed in BCC and hair follicles. We have then used reporter assays to investigate the effects of these isoforms on Gli1 transcriptional activity. We report that in BCC sections, PKCalpha but not PKCdelta was weakly expressed in the epidermis, whereas in the hair follicle, PKCalpha was expressed in the ORS and PKCdelta in the inner root sheath. In contrast, neither PKCalpha nor PKCdelta was expressed in BCC tumor islands, although both isoforms were often expressed in the surrounding stroma. In mammalian 293T cells, coexpression of constitutively active PKCalpha reduced the activity of Gli1 in a dose-dependent manner, whereas constitutively active PKCdelta increased the activity of Gli1, although this required higher expression levels. Regulation of mutant Gli1 protein localized exclusively to the nucleus was similar to that of the wild-type protein, indicating that nuclear-cytoplasmic shuttling is not a determinant of Gli1 control by either PKC isoform. Furthermore, PKC regulation of Gli1 did not involve activation of mitogen-activated protein kinase signaling. Finally, we show that exogenous Gli1 does not alter the expression of PKCalpha in human primary keratinocytes, suggesting that loss of this isoform in BCC is not via Hedgehog signaling. As BCCs have been proposed to originate from the ORS, loss of PKCalpha expression may be relevant to tumor formation; this may, in part, be because of the predicted increase in Gli1 transcriptional activity.
音猬因子信号通路的激活主要通过PTCH1基因的突变失活，与基底细胞癌（BCC）的发生相关。Gli1是Gli转录因子家族的成员之一，在BCC中表达，并且在转基因小鼠中，基底角质形成细胞中Gli1的靶向表达会导致BCC的发生。除了BCC，先前的研究表明Gli1在毛囊的外根鞘（ORS）中表达，但在毛囊间表皮中不存在。在本研究中，我们对在BCC和毛囊中表达的两种蛋白激酶C（PKC）亚型的表达模式进行了表征。然后，我们使用报告基因检测来研究这些亚型对Gli1转录活性的影响。我们报告，在BCC切片中，PKCα而非PKCδ在表皮中弱表达，而在毛囊中，PKCα在ORS中表达，PKCδ在内根鞘中表达。相反，PKCα和PKCδ在BCC肿瘤岛中均未表达，尽管这两种亚型通常在周围基质中表达。在哺乳动物293T细胞中，组成型活性PKCα的共表达以剂量依赖性方式降低Gli1的活性，而组成型活性PKCδ增加Gli1的活性，尽管这需要更高的表达水平。仅定位于细胞核的突变Gli1蛋白的调节与野生型蛋白相似，表明核质穿梭不是任一PKC亚型对Gli1进行调控的决定因素。此外，PKC对Gli1的调节不涉及丝裂原活化蛋白激酶信号的激活。最后，我们表明外源性Gli1不会改变人原代角质形成细胞中PKCα的表达，这表明BCC中该亚型的缺失并非通过刺猬因子信号通路。由于有人提出BCC起源于ORS，PKCα表达的缺失可能与肿瘤形成有关；这可能部分是由于预测的Gli1转录活性增加。
