Motility is rate-limiting for invasion of bladder carcinoma cell lines

Induced migration of tumor cells is generally considered to be one critical step in cancer progression to the invasive and metastatic stage. The implicit caveat of studies that show this is that other, unknown, signaling pathways and biophysical events are actually the operative rate-limiting steps, and not motility per se. Thus, to examine the hypothesis that motility is a single, but overall rate-limiting function required for invasion, disparate motility processes need be blocked with concordant effects on tumor invasion. Recently, we and others have described two signaling pathways that are critical to growth factor-induced motility but not mitogenesis. The key molecular switches are phospholipase C-gamma (PLCgamma) and calpain for cytoskeletal reorganization and rear detachment, respectively. We examined this hypothesis in a highly invasive tumor, bladder carcinoma. Three different human tumor cell lines, 253J-B-V, UMUC and T-24, were tested for invasiveness in vitro by transmigration of a Matrigel barrier. Inhibiting PLCgamma with the pharmacologic agent U73122 or the molecular dominant-negative PLCz construct reduced both invasiveness and motility. The same was noted when calpain was blocked using calpain inhibitor I (ALLN). These results demonstrate that one interventional target for limiting invasion is not necessarily an individual motility pathway but rather cell migration per se.