A role for the podosome/invadopodia scaffold protein Tks5 in tumor growth in vivo

Abstract

Podosomes and invadopodia are electron-dense, actin-rich protrusions located on the ventral side of the cellular membrane. They are detected in various types of normal cells, but also in human cancer cells and in Src-transformed fibroblasts. Previously we have shown that the scaffold protein Tks5 (tyrosine kinase substrate 5) co-localizes to podosomes/invadopodia in different human cancer cells and in Src-transformed NIH-3T3 cells. Upon reduced expression of Tks5 podosome formation is decreased, which leads to diminished gelatin degradation in vitro in various human cancer cell lines. It is unclear, however, whether cancer cells need podosomes for tumor growth and metastasis in vivo. To test this idea, we evaluated the ability of Srctransformed NIH-3T3 cells, showing stable reduced expression of Tks5 and podosome formation (Tks5 KD), to form subcutaneous tumors in mice. We demonstrate that decreased expression of Tks5 correlated with reduced tumor growth at this site. In addition, we generated lung metastases from these cells following tail vein injection. The lungs of mice injected i.v. with the Tks5 KD showed smaller-sized metastases, but there was no difference in the number of lesions compared to the controls, indicating that podosomes may not be required for extravasation from the blood stream into the lung parenchyma. Independent of the microenvironment however, the reduced tumor growth correlated with decreased tumor vascularization. Our data potentially implicate a novel role of podosomes as mediators of tumor angiogenesis and support further exploration of how podosome formation and Tks5 expression contribute to tumor progression.

XB130, a Novel Adaptor Protein, Promotes Thyroid Tumor Growth

“…3,4 Tyrosine kinase substrate 5 is a scaffolding adaptor protein with five Src homology 3 (SH3) domains, co-localizes to podosomes, and regulates migration and invasion of various human cancer cells. 5,6 These findings support a broader investigation of the effects of adaptor proteins on tumorigenesis and their potential as diagnostic biomarkers and therapeutic targets of cancer.…”

Automated Podosome Identification and Characterization in Fluorescence Microscopy Images

“…With lifetimes between 2-12 min, podosomes are very dynamic and continuously change size, shape, and composition~Destaing et al, 2003;Evans et al, 2003!. They have initially been identified in Src-transformed fibroblasts, and although previously thought to be restricted to only a few cell types, they have now been observed in smooth muscle cells, activated endothelial cells, and cells of the myeloid lineage such as osteoclasts, macrophages, and dendritic cells DCs!~Murphy & Courtneidge, 2011!. More recently, podosome-associated structures named invadopodia have been found on the ventral membranes of tumor cells where they are thought to play a central role in tumor metastasis Blouw et al, 2008;Mukhopadhyay et al, 2009!. Most of our current understanding of podosome formation, turnover, and distribution is based on studies that exploit conventional and confocal microscopy techniques. Although these techniques are potentially quantitative, largescale image analysis is required to obtain enough statistical power to be able to detect subtle and transient variations in podosome composition.…”

Membrane lipids in invadopodia and podosomes: Key structures for cancer invasion and metastasis

“…Tks5 is an adaptor protein with an N-terminal phox homology (PX) domain, which was originally identified as an Src substrate [79]. Both Tks5 and its relative, Tks4, have been shown to play important roles in podosome formation, matrix degradation, and tumor growth in vivo [80][81][82][83]. Recently, they have been shown to mediate the generation of reactive oxygen species (ROS) at the invadopodia of cancer cells, which is required for invadopodia formation and cancer cell invasion [84,85].…”