Department of Pathology, BIDMC/Harvard Medical School, Boston, MA 02215, USA.
Lab Invest. 2011 Oct;91(10):1414-26. doi: 10.1038/labinvest.2011.104. Epub 2011 Jul 18.
Hemidesmosomes (HDs) are multiprotein structures that anchor epithelia to the basement membrane. During squamous cell carcinoma (SCC) invasion, there is a reduction in the number of HDs, which may facilitate dissemination. Mechanisms of HD disassembly are incompletely understood. Previous work has shown that epidermal growth factor (EGF)-induced phosphorylation of the β4 integrin on three of its serines, S(1356)S(1360)S(1364), can induce HD disassembly in normal cells. Here, we examine the role of β4 integrin serine phosphorylation in SCC. We have found that around 60% of invasive cutaneous SCC show increased β4 phosphorylation on S(1356) when compared with carcinoma in situ or normal tissue. To assess the mechanisms by which SCC increases β4 phosphorylation, we performed in vitro analyses. Compared with keratinocytes, SCC cells showed increased levels of S(1356) phosphorylation in the absence of EGF, correlating with reduced HD-like structures. In addition, phospho-S(1356) signal was largely segregated from other HD components. Epidermal growth factor receptor and PKC inhibitors inhibited basal levels of S(1356) phosphorylation in SCC, suggesting that cells use intrinsic mechanisms to activate the EGF signaling pathway to induce β4 phosphorylation. Moreover, these inhibitors stabilized HD-like structures in SCC cells and reduced their migratory ability. Mutation of S(1356)S(1360)S(1364) in SCC cells to non-phosphorylatable alanines stabilized HD-like structures and substantially reduced migration, while mutation into phosphorylation mimicking aspartate reduced HD-like structures but had no effect on migration, suggesting that serine phosphorylation function is releasing anchorage rather than promoting migration. Altogether these results suggest that β4 serine phosphorylation may have an important role during SCC invasion by destabilizing HDs and facilitating migration.
半桥粒（HDs）是将上皮组织锚定到基底膜的多蛋白结构。在鳞状细胞癌（SCC）侵袭过程中，HDs 的数量减少，这可能有助于扩散。HD 解体的机制尚不完全清楚。以前的工作表明，表皮生长因子（EGF）诱导β4 整合素三个丝氨酸（S1356S1360S1364）的磷酸化可以诱导正常细胞中的 HD 解体。在这里，我们研究了β4 整合素丝氨酸磷酸化在 SCC 中的作用。我们发现，与原位癌或正常组织相比，大约 60%的侵袭性皮肤 SCC 在 S1356 上显示出β4 磷酸化增加。为了评估 SCC 增加β4 磷酸化的机制，我们进行了体外分析。与角质形成细胞相比，SCC 细胞在没有 EGF 的情况下表现出更高水平的 S1356 磷酸化，这与 HD 样结构减少相关。此外，磷酸化 S1356 信号主要与其他 HD 成分分离。EGF 受体和 PKC 抑制剂抑制 SCC 中的基础水平 S1356 磷酸化，表明细胞使用内在机制激活 EGF 信号通路诱导β4 磷酸化。此外，这些抑制剂稳定了 SCC 细胞中的 HD 样结构并降低了它们的迁移能力。将 SCC 细胞中的 S1356S1360S1364 突变为非磷酸化的丙氨酸稳定了 HD 样结构并大大降低了迁移，而突变为磷酸化模拟天冬氨酸则降低了 HD 样结构，但对迁移没有影响，表明丝氨酸磷酸化功能是释放锚定而不是促进迁移。总之，这些结果表明，β4 丝氨酸磷酸化可能通过破坏 HD 并促进迁移在 SCC 侵袭中起重要作用。
