Research Summary

Integrin-dependent Regulation of Anchorage Independence in Cancers

Integrin mediated adhesion of cells to the extracellular matrix regulates growth factor mediated signaling to support anchorage dependence. Cancer cells overcome this regulatory control to become anchorage independent, supporting tumor formation and metastasis. Understanding how adhesion regulates growth signaling and how cancer cells overcome this regulation, is important to our knowledge of how cancers are caused and eventually treated. Earlier work has identified the adhesion dependent plasma membrane localization of membrane raft microdomains to regulate anchorage independent growth signaling (Erk, Akt, Rac signaling). On loss of adhesion membrane raft microdomains are rapidly endocytosed, and cleared from the plasma membrane to turn off anchorage dependent signaling. This is mediated by the adhesion dependent regulation of caveolar endocytosis and exocyst-dependent exocytosis. Cancer cells by deregulating caveolar endocytois and / or promoting exocyst-dependent exocytosis could support anchorage independent signaling. Understanding the adhesion dependent regulation of caveolin-1 function (as part of or independent of caveolae), Ral and Arf6 function (as part of the exocyst complex) and their significance in cancers is the focus of my labs research. Our studies have since shown that Ral works upstream of Arf1 to regulate its activation and function in normal and cancer cells, through the Ral effector RalBP1.  
 
Having established the presence of a Ral-Arf6 crosstalk downstream of integrin and oncogenic Ras we asking how this crosstalk helps mediated delivery of exocytic vesicles at the plasma membrane and its role in other Ral dependent cellular functions.  We are also interested in the role Ral effectors (beyond RalBP1) have in mediating this crosstalk and Ral dependent signaling. We are also evaluating how RalGEFs, GAPs and Aurora kinase A contribute to adhesion and oncogenic Ras dependent Ral activation and function.  
 
In collaboration with Dr.Jayakannan’s lab we have also develope a novel self assembling dextran based drug delivery systems for delivering poorly soluble drugs specifically to cancer cells. We also developed fluorescently tagged dextra nanovesicles to eveluate their differential uptake in cancer cells and identified cell lines that preferentially take up the nanovesicle.  Using this delivery system we now have created nanovesicles with the Aurora kinases inhibitor MLN8237 that significantly improves drug delivery and specificity for Aurora Kinase A.  We are aiming to use the same to target RalA downstream to disrupt cancer cell anchorage independence. 
 
We are also extending these studies to understand how 3D microenvironments, their crosslinking and stiffness regulates cellular endocytosis and signaling. The role caveolae and their regulation of membrane tension and mobility and its role in mediating the same is also of direct interest to us.  This involves optimizing techniques and tools for visualizing cells in 3D and quantitative measurements of membrane mobility and endocytosis in 3D.