Cdc42-interacting protein family adaptors regulate endocytosis, membrane trafficking, migration, and invasion in cancer cells.

摘要

Timely and spatially controlled endosomal trafficking and signaling is important for cell proliferation, directed cell migration, and cell invasion, which are frequently misregulated in cancer cells. Cdc42-interacting protein-4 (CIP4) family adaptors promote endocytosis by inducing membrane invaginations via their Fer/CIP4 Homology-Bin/Amphyphysin/Rvs (F-BAR) domains, coupled with activation of the actin assembly machinery to promote vesicle fusion or motility. My thesis focuses on defining the roles of CIP4, and a related protein, Transducer of Cdc42-mediated actin assembly-1 (Toca-1), in regulating Epidermal Growth Factor Receptor (EGFR) endocytosis, EGFR trafficking, cancer cell motility, and invasion. In Chapter 2, I show that CIP4 and Toca-1 localize to early endosomes and promote EGFR trafficking from early endosomes to lysosomes for degradation, thus limiting extracellular signal-regulated kinase signaling from early endosomes and proliferation of A431 carcinoma cells. In Chapter 3, I provide novel evidence that depletion of Toca-1 results in defects in actin-based lamellipodial protrusions that are required for cell motility. The cause of these defects may relate to altered recruitment of the Abelson-interactor-1 and its effector Wiskott-Aldrich syndrome protein family verprolin-homologous protein to the lamellipodia in A431 cells depleted of Toca-1. Results in Chapter 4 identify CIP4 as a negative regulator of breast cancer invasiveness downstream of Src protein-tyrosine kinase. Src is a potent inducer of extracellular matrix (ECM)-degrading structures called invadopodia that function in tissue invasion by cancer cells. I found that CIP4 is a Src substrate that localizes to Src-induced invadopodia in MDA-MB-231 breast cancer cells. Interestingly, depletion of CIP4 results in enhanced ECM degradation, invadopodia formation, and invasiveness compared to control cells. Thus, CIP4 and Toca-1 are multifaceted regulators of EGFR downregulation, EGF-induced cell motility, and Src-induced cell invasion.