Dermatology Section, School of Medicine, Dentistry and Nursing, College of Medical, Veterinary and Life Sciences, Glasgow University, Glasgow, UK.
Oncogene. 2014 Aug 7;33(32):4132-43. doi: 10.1038/onc.2013.372. Epub 2013 Sep 16.
To investigate tumour progression mechanism in transgenic mouse skin carcinogenesis, inducible PTEN ablation (Δ5PTEN(flx)) was targeted to the epidermis of mice expressing activated ras(Ha)/fos oncogenes (HK1.ras and HK1.fos). RU486-treated HK1.ras/fos-Δ5PTEN(flx) epidermis exhibited significant keratinocyte proliferation resulting in hyperplasia and proliferating cysts. While HK1.ras/fos-Δ5PTEN(flx) papillomatogenesis was accelerated, malignant conversion was delayed and tumours exhibited well-differentiated squamous cell carcinoma (wdSCC) histotypes, suggesting inhibition of early-stage malignant progression. Immediate elevated p53/p21 expression was observed in HK1.ras/fos-Δ5PTEN(flx) hyperplasia, cysts and papillomas, and while malignant conversion required p53 loss, elevated p21 expression persisted in most wdSCCs to limit further progression, unless p21 was also lost and wdSCC progressed to more aggressive carcinomas. In contrast, TPA-promoted (that is, c-fos-activated) bi-genic HK1.ras-Δ5PTEN(flx) cohorts lost p53/p21 expression during early papillomatogenesis and rapidly produced poorly differentiated carcinomas (pdSCCs) with high BrdU-labelling and elevated cyclin D1/E2 expression levels, indicative of a progression mechanism driven by failures in cell-cycle control. Intriguingly, HK1.ras/fos-Δ5PTEN(flx) wdSCCs did not exhibit similar failures, as western and immunofluorescence analysis found downregulated cyclin E2 whenever p21 persisted; further, while westerns detected elevated cyclin D1, immunofluorescence identified reduced expression in proliferative basal layer nuclei and a redistributed expression profile throughout p21-positive wdSCC keratinocytes. These data demonstrate that rapid early epidermal responses to ras(Ha)/fos/ΔPTEN co-operation involve induction of p53/p21 to alter differentiation and divert excessive proliferation into cyst formation. Further, despite three potent oncogenic insults p53 loss was required for malignant conversion, and following p53 loss persistent, p53-independent p21 expression possessed the potency to limit early-stage malignant progression via cyclin D1/E2 inhibition.
为了研究转基因小鼠皮肤癌发生中的肿瘤进展机制，将诱导型 PTEN 缺失（Δ5PTEN(flx)）靶向表达激活的 ras(Ha)/fos 癌基因（HK1.ras 和 HK1.fos）的小鼠表皮。用 RU486 处理的 HK1.ras/fos-Δ5PTEN(flx)表皮表现出明显的角质形成细胞增殖，导致增生和增殖性囊肿。虽然 HK1.ras/fos-Δ5PTEN(flx)的乳头瘤形成加速，但恶性转化延迟，肿瘤表现出分化良好的鳞状细胞癌（wdSCC）组织学类型，表明早期恶性进展受到抑制。在 HK1.ras/fos-Δ5PTEN(flx)增生、囊肿和乳头瘤中立即观察到 p53/p21 表达升高，而恶性转化需要 p53 丧失，p21 表达在大多数 wdSCC 中持续升高以限制进一步进展，除非 p21 也丧失，并且 wdSCC 进展为更具侵袭性的癌。相比之下，TPA 促进的（即 c-fos 激活的）双基因 HK1.ras-Δ5PTEN(flx)队列在早期乳头瘤形成过程中丧失了 p53/p21 表达，并迅速产生低分化的癌（pdSCC），具有高 BrdU 标记和升高的细胞周期蛋白 D1/E2 表达水平，表明进展机制是由细胞周期控制失败驱动的。有趣的是，HK1.ras/fos-Δ5PTEN(flx)的 wdSCC 并没有表现出类似的失败，因为 Western 和免疫荧光分析发现，只要 p21 持续存在，细胞周期蛋白 E2 就下调；此外，尽管 Western 检测到细胞周期蛋白 D1 升高，但免疫荧光鉴定出增殖基底细胞核中的表达减少，并在 p21 阳性 wdSCC 角质形成细胞中重新分布表达谱。这些数据表明，快速的早期表皮对 ras(Ha)/fos/ΔPTEN 合作的反应涉及诱导 p53/p21 改变分化并将过度增殖转移到囊肿形成。此外，尽管存在三种强烈的致癌作用，但 p53 丧失是恶性转化所必需的，并且在 p53 丧失后，持续存在的、与 p53 无关的 p21 表达通过抑制细胞周期蛋白 D1/E2 具有限制早期恶性进展的潜力。
