Abstract
Interaction of breast cancer cells (BCCs) with stromal components is critical for tumor growth and metastasis. Here, we assessed the role of CD9 in adhesion, migration and invasiveness of BCCs. We used co-cultures of BCCs and bone marrow-derived multipotent mesenchymal stromal cells (MSCs), and analyzed their behavior and morphology by dynamic total internal reflection fluorescence, confocal and scanning electron microscopy. 83, 16 and 10% of contacts between MDA-MB-231 (MDA), MA-11 or MCF-7 cells and MSCs, respectively, resulted in MSC invasion. MDA cells developed long magnupodia, lamellipodia and dorsal microvilli, whereas long microvilli emerged from MA-11 cells. MCF-7 cells displayed large dorsal ruffles. CD9 knockdown and antibody blockage in MDA cells inhibited MSC invasion by 95 and 70%, respectively, suggesting that CD9 is required for this process. Remarkably, CD9-deficient MDA cells displayed significant alteration of their plasma membrane, harboring numerous peripheral and dorsal membrane ruffles instead of intact magnupodium/lamellipodium and microvillus, respectively. Such modification might explain the delayed adhesion, and hence MSC invasion. In agreement with this hypothesis, CD9-knockdown suppressed the metastatic capacity of MDA cells in mouse xenografts. Our data indicate that CD9 is implicated in BCC invasiveness and metastases by cellular mechanisms that involve specific CD9+ plasma membrane protrusions of BCCs.
Highlights
The formation of breast cancer metastases requires an interaction in the tumor microenvironment between malignant epithelia and local stroma [1, 2]
MDA-MB-231 and MCF-7 breast cancer cells (BCCs) displayed a heterogeneous expression of CD9 which comprised 74, 19 and 59% of total cells, respectively (Fig. 1A, blue)
We evaluated the number of CD9+ plasma membrane protrusions (PMPs) emerging from MDA, MA-11 and MCF-7 cells transfected with CD9-GFP fusion plasmid by confocal microscopy (Fig. 6)
Summary
The formation of breast cancer metastases requires an interaction in the tumor microenvironment between malignant epithelia and local stroma [1, 2]. In order to adhere to, communicate with, and transfer materials to/ from stromal cells, breast cancer cells (BCCs) often employ different types of plasma membrane protrusions (PMPs), including filopodia and lamellipodia [3]. Tetraspanin-29 (CD9, motility-related protein-1) is involved in the metastatic process and depending on the context as a metastasis suppressor or promoter [12] It is involved in cell fusion, adhesion, motility, proliferation, and signaling [13] and is required for egg-sperm fusion leading to fertilization [14, 15]. Upon transplantation of CD9-deficient cells in a murine model, an inhibition of tumor growth was observed after one week as well as a partial loss of metastatic capacity These novel CD9 functions could be exploited to develop innovative breast cancer therapeutic strategies
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
