Identification of Novel Proteins Interacting with LATS1/2 During Tumorigenesis and Anti-Tubulin Drug Response

Abstract

The Hippo pathway is a signaling cascade that plays essential roles in organisms such as development, organ size control, stem cell differentiation and renewal, as well as important processes necessary for cancer development and progression. Within the core cassette of the pathway are LATS1 and LATS2, serine/threonine kinases with a continually expanding repertoire of functions and effectors that relay upstream tumor suppressive signals. Despite the plethora of studies investigating Hippo pathway signaling, few LATS1/2 interacting proteins have been identified. In this thesis, the regulatory networks surrounding LATS1/2 are explored. By screening the Nedd4-like family E3 ubiquitin ligases, WWP1 was identified as a novel negative regulator of LATS1 by ubiquitinating and promoting its degradation by the 26S proteasome pathway. Importantly, loss of LATS1 stability was shown to be critical for WWP1-induced increases in cell proliferation and anchorage-independent growth of breast cancer cells. Furthermore, a novel signaling axis involving Cdk1, LATS2 and Pin1 was identified. After anti-tubulin drug treatment, activated Cdk1 kinase can directly phosphorylate LATS2 at five sites which subsequently binds Pin1 and inactivates its anti-apoptotic function. Lastly using CRISPR/Cas9 functional genomics screening, novel genes that promoted LATS2-induced S-phase cell cycle accumulation in lung cancer cells were identified and validated. Collectively these findings uncover novel upstream regulators and downstream mediators of LATS1/2 in functions related to tumorigenesis and drug response. The novel interacting proteins identified in this work may serve as potential new biomarkers for breast and lung cancer progression as well as anti-tubulin drug sensitivity. Thus mapping the molecular network of the Hippo pathway, with emphasis on the bona fide tumor suppressors LATS1/2, may have significant implications for the prognosis and treatment of breast and lung cancers.