Project Abstract/Summary
Cancer is the second leading cause of death in the United States. Overall survival for patients with tumors
that remain localized to the tissue of origin remain relatively high, while it is estimated that 90% of all cancer
related deaths are due to metastatic dissemination to secondary sites. This underscores the importance of
identifying signaling pathways that promote metastasis. Mitochondria are multifunctional organelles with
important roles in regulating many cellular processes outside of ATP production and are recognized for their
roles in tumorigenesis and metastasis. This project seeks to define a novel mechanism that promotes tumor cell
invasion and metastasis through a previously unidentified signaling pathway between Mitochondrial Rho GTPase
2 (MIRO2) and atypical myosin IXB (MYO9B).
MIRO2 is an outer-mitochondrial membrane protein that is a part of the MIRO subfamily of Ras GTPases.
MIROs were first characterized in neurons where they are involved in the anterograde and retrograde trafficking
of mitochondria. MIRO2 has been shown by several groups to be dispensable for mitochondrial trafficking in
many non-neuronal cell types. Our lab has previously shown that MIRO2 mRNA is enriched in tumorigenic
tissues in many tumor types when compared to normal tissue. Additionally, we have shown in prostate cancer
that MIRO2 is important in tumor cell viability, anchorage-dependent and -independent growth, and tumor growth
in vivo. Despite this initial evidence, it remains unknown if MIRO2 exclusively impacts the primary tumor or if this
is also important in metastasis. My initial results show that loss of MIRO2 reduces the invasive capacity of tumor
cells from many tumor types including breast, melanoma, pancreas, and prostate. Furthermore, I have shown
out of the top newly identified MIRO2 binding partners, loss of MYO9B reduces invasive capacity to the greatest
extent. MYO9B is known to control cell motility by localizing to the leading edge of migrating cells and inactivating
RhoA through MYO9B’s Rho GTPase activating protein (GAP) domain. Excitingly, I show that loss of both MIRO2
and MYO9B result in increased active RhoA. Given this evidence, I hypothesize MIRO2 promotes tumor cell
invasion and metastasis through positively regulating MYO9B GAP activity.
In this proposal I will 1) determine the role of MIRO2 in tumor cell invasion and metastasis and 2)
determine the mechanism in which MIRO2 regulates tumor cell invasion. This proposal will utilize many models
including, but not limited to: 2D/3D in vitro invasion systems, live cell imaging of migrating cells, in vivo breast
cancer metastasis models, cell-free GTPase assays, co-immunoprecipitation, and proximity ligation assays.
Overall, the goal of this proposal is to serve as the basis for the development of novel therapeutics to target
metastatic disease.