Differential Tks5 isoform expression contributes to metastatic invasion of lung adenocarcinoma

Abstract

Metastasis accounts for the vast majority of cancer-related deaths, yet the molecular mechanisms that drive metastatic spread remain poorly understood. Here we report that Tks5, which has been linked to the formation of proteolytic cellular protrusions known as invadopodia, undergoes an isoform switch during metastatic progression in a genetically engineered mouse model of lung adenocarcinoma. Nonmetastatic primary tumor-derived cells predominantly expressed a short isoform, Tks5 short , while metastatic primary tumor-and metastasis-derived cells acquired increased expression of the full-length isoform Tks5 long . This elevation of Tks5 long to Tks5 short ratio correlated with a commensurate increase in invadopodia activity in metastatic cells compared with nonmetastatic cells. Further characterization of these isoforms by knockdown and overexpression experiments demonstrated that Tks5 long promoted invadopodia in vitro and increased metastasis in transplant models and an autochthonous model of lung adenocarcinoma. Conversely, Tks5 short decreased invadopodia stability and proteolysis, acting as a natural dominant-negative inhibitor to Tks5 long . Importantly, high Tks5 long and low Tks5 short expressions in human lung adenocarcinomas correlated with metastatic disease and predicted worse survival of early stage patients. These data indicate that tipping the Tks5 isoform balance to a high Tks5 long to Tks5 short ratio promotes invadopodia-mediated invasion and metastasis.

The CD44s splice isoform is a central mediator for invadopodia activity

“…CD44s is required for cortactin phosphorylation and interacts with MT1-MMP at sites of invadopodia. In addition to our findings on the requirement of splice isoforms in the activity of invadopodia, a recent study has shown that a specific Tks5-long isoform, generated by the use of an alternative transcription start site, promotes invadopodiamediated metastasis, whereas the Tks5-short isoform inhibits it (Li et al, 2013). That and our studies indicate that biological processes are, in many cases, regulated at the level of protein isoforms encoded by the same gene.…”

“…Accumulating evidence has shown that invadopodia are crucial structures for ECM degradation, and subsequent tumor cell migration and invasion Eckert et al, 2011;Li et al, 2013;Paz et al, 2013;Seals et al, 2005). Invadopodia are small dot-shaped actin-rich protrusions that are in close contact with ECM (Murphy and Courtneidge, 2011).…”

Regulation of invadopodia by the tumor microenvironment

“…53 Although no concrete evidence has yet demonstrated the presence of invadopodia in vivo, several key invadopodia proteins, such as Tks5, cortactin, and N-WASP, are necessary for tumor growth and metastasis in mouse cancer models. [52][53][54][55][56] Here, we assess the role of the tumor microenvironment in the regulation of invadopodia formation and function and how this relates to cancer progression and metastasis. We discuss recent data demonstrating how inputs from the tumor microenvironment, such as stromal-cell interactions, growth factors, hypoxia, pH, and metabolism, alter invadopodia biology and the implications for the surrounding components subject to these signaling changes.…”

Invadopodia and basement membrane invasion in vivo

“…The advantages in imaging, biochemical approaches, and genetic and pharmacological perturbations in 2D conditions have led to remarkable advances in our understanding of invadopodia. 22,[39][40][41][42] These findings include the identification of different components of invadopodia, [43][44][45] elucidation of the stages of invadopodia formation, [46][47][48][49] identification of genes associated with cancer metastasis that regulate invadopodia formation, 19,21,[50][51][52] understanding of the trafficking of proteases to invadopodia, [53][54][55][56][57] and examination of invadopodia membrane dynamics. 58 Key insights have also been gained into the regulation of their formation by growth factors, integrin activation, and the microenvironment, including hypoxia, matrix stiffness, Over 20 years ago, protrusive, F-actin-based membrane structures, termed invadopodia, were identified in highly metastatic cancer cell lines.…”