Loss of ASAP1 in the MMTV-PyMT model of luminal breast cancer activates AKT, accelerates tumorigenesis, and promotes metastasis.

ASAP1 is a multi-domain adaptor protein that regulates cytoskeletal dynamics, receptor recycling and intracellular vesicle trafficking. Its expression is associated with poor prognosis in a variety of cancers, and can promote cell migration, invasion and metastasis. Although amplification and expression of ASAP1 has been associated with poor survival in breast cancer, we found that in the autochthonous MMTV-PyMT model of luminal breast cancer, ablation of ASAP1 resulted in an earlier onset of tumor initiation and increased metastasis. This was due to tumor cell-intrinsic effects of ASAP1 deletion, as ASAP1 deficiency in tumor, but not in stromal cells was sufficient to replicate the enhanced tumorigenicity and metastasis observed in the ASAP1-null MMTV-PyMT mice. Loss of ASAP1 in MMTV-PyMT mice had no effect on proliferation, apoptosis, angiogenesis or immune cell infiltration, but enhanced mammary gland hyperplasia and tumor cell invasion, indicating that ASAP1 can accelerate tumor initiation and promote dissemination. Mechanistically, these effects were associated with a potent activation of AKT. Importantly, lower ASAP1 levels correlated with poor prognosis and enhanced AKT activation in human ER+/luminal breast tumors, validating our findings in the MMTV-PyMT mouse model for this subtype of breast cancer. Taken together, our findings reveal that ASAP1 can have distinct functions in different tumor types and demonstrate a tumor suppressive activity for ASAP1 in luminal breast cancer.

Loss of ASAP1 in mice impairs adipogenic and osteogenic differentiation of mesenchymal progenitor cells through dysregulation of FAK/Src and AKT signaling.

ASAP1 is a multi-domain adaptor protein that regulates cytoskeletal dynamics, receptor recycling and intracellular vesicle trafficking. Its expression is associated with poor prognosis for a variety of cancers, and promotes cell migration, invasion and metastasis. Little is known about its physiological role. In this study, we used mice with a gene-trap inactivated ASAP1 locus to study the functional role of ASAP1 in vivo, and found defects in tissues derived from mesenchymal progenitor cells. Loss of ASAP1 led to growth retardation and delayed ossification typified by enlarged hypertrophic zones in growth plates and disorganized chondro-osseous junctions. Furthermore, loss of ASAP1 led to delayed adipocyte development and reduced fat depot formation. Consistently, deletion of ASAP1 resulted in accelerated chondrogenic differentiation of mesenchymal cells in vitro, but suppressed osteo- and adipogenic differentiation. Mechanistically, we found that FAK/Src and PI3K/AKT signaling is compromised in Asap1GT/GT MEFs, leading to impaired adipogenic differentiation. Dysregulated FAK/Src and PI3K/AKT signaling is also associated with attenuated osteogenic differentiation. Together these observations suggest that ASAP1 plays a decisive role during the differentiation of mesenchymal progenitor cells.