Abstract:
Breast cancer is one of the most commonly diagnosed cancers in women around the
world. In general, the more aggressive the tumor, the more rapidly it grows and the
more likely it metastasizes. Cell migration, is a complex process, which requires the
dynamic regulation of actin cytoskeleton. Members of the Rho subfamily of small GTPbinding
proteins (GTPases) play a central role in breast cancer cell motility. The switch
between active GTP-bound and inactive GDP-bound state is regulated by Guanine
nucleotide exchange factors (GEFs), GTPase-activating proteins (GAPs) and Guaninenucleotide
dissociation inhibitors (GDIs). Here we study the role of StarD13, a newly
identified Rho-GAP that specifically inhibits the function of RhoA and Cdc42. We aim
to investigate its role in breast cancer proliferation and metastasis. The level of
expression of this Rho-GAP in tumor tissues of different grades is assayed using
immunohistochemistry. Moreover, the role of StarD13 in breast cancer cell lines is
studied using two approaches. StarD13 is overexpressed using a StarD13-GFP
construct, in the second approach StarD13 is knocked down using a specific siRNA.
The effect on the activity of Rho-GTPases is observed using pull down activation assay,
which confirmed StarD13 as a negative regulator for Rho and Cdc42 but not for Rac.
Our results also showed that StarD13 plays a negative role in cellular proliferation.
Moreover to investigate the role of StarD13 in cell motility, StarD13 knock down
resulted in an inhibition of cell motility and cells were not able to detach their tail and
move forward. Being a Rho-GAP and localizing to focal adhesions, we hypothesize that
StarD13 is inhibiting Rho to allow the formation of Rac-dependent focal complexes and
the detachment of focal adhesions for the cells to move forward. However, our results
show that the knockdown of StarD13 seems to promote breast cancer cell invasion in
vitro.
