Abstract P5-05-01: Physico-biochemical regulation of EMT by microtubule associated protein 7 (MAP7)
Authors: Choi DS , Dave B , Rosato RR , Chang JC 
Published: March 2017

Background: We previously reported about 500 cancer stem cell (CSC) specific gene signatures from patient tumor samples. After screening with shRNAs for the 500 genes affecting mammosphere forming ability, we identified microtubule-assoicated protein 7 (MAP7) as one of the top candidate genes, which may serve as a target for breast CSCs. Although MAP7 is a predominant epithelial microtubule binding protein, only limited number of reports suggests that MAP7 may be a regulator of microtubule dynamics during cell division and a cofactor of Kinesin-1 in compartment transport in cells. However, little is known about how MAP7 supports epithelial cancers, especially breast cancer. Previously, we have reported that the mammosphere forming cells exhibit treatment resistance and high metastatic potential, which are intrinsic characters for CSCs displaying epithelial mesenchymal transition (EMT). We hypothesize that MAP7 supports breast cancer progression by promoting CSC self-renewal and survival through regulation of EMT.

Objectives: Here, we aim to show that MAP7 is an essential regulator of breast CSCs and to elucidate mechanism behind EMT regulation by MAP7 in breast CSCs.

Methods and Results: On Oncomine database analysis, MAP7 was up-regulated in most epithelial cancers, when compared to the corresponding normal tissues. Similarly, its expression in breast cancer was 2-fold higher than in the normal breast tissue (p&lt;0.05), but without significant variances in the expression across the breast cancer subtypes. Gene silencing of MAP7 significantly reduced CD44+/CD24- breast CSC populations and mammosphere forming efficiencies of MDA-MB-231, HCC1937, and MDA-MB-468 breast cancer cells. Furthermore, the silencing of MAP7 expression compromised invasive potential of MDA-MB-231 cells by 50% and significantly altered the cell membrane mechanics of MDA-MB-468 cells, as indicated by a high-content image analysis for cell shapes and cell adhesion efficiency. More importantly, delivery of siRNA in vivo inhibited the growth of BCM2147 patient-derived tumor, and limiting dilution assay demonstrated that the tumor initiation potential of BCM2147 can be eliminated by MAP7 silencing. Through confocal microscope analysis of images of fluorescent immunostaining and co-immunoprecipatation assays, MAP7 showed polarized-expressions in spindle-shaped cancer cells and was co-localized with Focal Adhesion Kinase (FAK). Moreover, MAP7 silencing inhibited the phosphorylation of FAK by inactivating p130CAS and JSAP1, the upper stream and the down-stream regulators of FAK.

Conclusion: We have showed the ectopic expression of MAP7 in breast tumors and other epithelial tumors, suggesting MAP7 may be involved in tumorigenesis and critical for the survival of tumor cells. Moreover, our results suggest that MAP7 is a key element for survival and self-renewal of breast CSCs through polarization of cells and activation of FAK, required for the initiation of EMT. To that end, here we report that MAP7 is essential for breast cancer growth by supporting CSC survival and self-renewal.

Citation Format: Choi DS, Dave B, Rosato RR, Chang JC. Physico-biochemical regulation of EMT by microtubule associated protein 7 (MAP7) [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P5-05-01.