Cancer stem cells (CSC) play a pivotal role in
cancer metastasis and resistance to
therapy. Previously, we compared the phosphoproteomes of
breast cancer stem cells (BCSCs) enriched subpopulation and non-BCSCs sorted from
breast cancer patient-derived xenograft (PDX), and identified a function unknown
protein, transmembrane and coiled-coil domain family 3 (TMCC3) to be a potential enrichment marker for BCSCs. We demonstrated greater expression of TMCC3 in BCSCs than non-BCSCs and higher expression of TMCC3 in metastatic lymph nodes and lungs than in primary
tumor of
breast cancer PDXs. TMCC3 silencing suppressed mammosphere formation, ALDH activity and cell migration in vitro, along with reduced tumorigenicity and
metastasis in vivo. Mechanistically, we found that AKT activation was reduced by TMCC3 silencing, but enhanced by TMCC3 overexpression. We further demonstrated that TMCC3 interacted directly with AKT through its 1-153 a.a. domain by cell-free biochemical assay in vitro and co-immunoprecipitation and interaction domain mapping assays in vivo. Based on domain truncation studies, we showed that the AKT-interacting domain of TMCC3 was essential for TMCC3-induced AKT activation, self-renewal, and
metastasis. Clinically, TMCC3
mRNA expression in 202
breast cancer specimens as determined by qRT-PCR assay showed that higher TMCC3 expression correlated with poorer clinical outcome of
breast cancer, including early-stage
breast cancer. Multivariable analysis identified TMCC3 expression as an independent risk factor for survival. These findings suggest that TMCC3 is crucial for maintenance of BCSCs features through AKT regulation, and TMCC3 expression has independent prognostic significance in
breast cancer. Thus, TMCC3 may serve as a new target for
therapy directed against CSCs.