Beaumont, K. A. | Search bioRxiv

bioRxiv2020

Functional melanoma cell heterogeneity is regulated by MITF-dependent cell-matrix interactions

Phenotypic heterogeneity of cancer cells plays a critical role in shaping treatment response. This type of heterogeneity is organized spatially with specific phenotypes, such as sharply demarcated clusters of proliferating and cell cycle-arrested cells, predominating within discrete domains within a tumor. What determines the occurrence of specific tumor cell phenotypes in distinct microdomains of solid cancers is poorly understood. Here, we show that in melanoma spatial organization of phenotypic heterogeneity is dictated by the expression and activity of MITF. We reveal that this lineage survival oncogene controls ECM composition and organization, and ROCK-driven mechanotransduction through focal adhesion maturation and actin cytoskeleton functionality. In turn, altered tumor microarchitecture and structural integrity impact tumor solid stress which then mediates phenotypic heterogeneity through p27Kip1. Rho-ROCK-myosin signaling is necessary to transmit the effect of the reciprocal cell-ECM regulation into phenotypic heterogeneity. Our findings place cell-ECM crosstalk as a central driver of phenotypic tumor heterogeneity. SignificancePhenotypic heterogeneity is a major culprit of cancer therapy failure. We demonstrate that phenotypic heterogeneity is controlled through tumor cell-ECM crosstalk resulting in altered tumor microarchitecture, mechanotransduction and Rho-ROCK-myosin signaling. Melanoma shares these physical properties with any solid cancer underscoring the importance of our findings for therapeutically targeting this phenomenon.

cancer biology↗

bioRxiv2019

Abrogation of RAB27A expression transiently affects melanoma cell proliferation

The role of the small GTPase RAB27A as an essential melanosome trafficking regulator in melanocytes is well-accepted. A decade ago, RAB27A was identified as a tumor dependency gene that promotes melanoma cell proliferation. RAB27A has since been linked to another propeller of cancer progression: exosome secretion. We have recently demonstrated that RAB27A is overexpressed in a subset of melanomas. High RAB27A gene and protein expression correlates with poor prognosis in melanoma patients. Mechanistic investigations revealed that the generation of pro-invasive exosomes was RAB27A-dependent and, therefore, silencing RAB27A reduced melanoma cell invasion in vitro and in vivo. However, previous studies have implicated RAB27A to be involved in both proliferation and invasion of melanoma cells. In this study, we demonstrate that the effects of abrogating RAB27A expression on proliferation are temporary, in contrast to the previously reported persistent effects on tumor invasion and metastasis. Therefore, we assist in the dissection of the short-term versus long-term effects of RAB27A knockdown on melanoma cell proliferation, invasion, and metastasis. We believe that our findings provide novel insights into the effects of RAB27A blockade. SignificanceRAB27A is known to serve as an essential regulator for melanosome trafficking. However, to date its role in melanoma biology has not been completely deciphered. While there are consistent independent reports on the pro-invasive effects of RAB27A, there are conflicting data on its impact on cell proliferation. Here we show that indeed abrogation of RAB27A does reduce cellular proliferation; however, this effect is only transient, while the impact on invasion as reported previously is persistent. This finding offers an explanation for the apparent contradiction in the literature and provides a deeper understanding of RAB27A function in melanoma cell biology.

cancer biology↗