The transmembrane
glycoprotein, CUB (
complement C1r/C1s, Uegf, Bmp1) domain-containing
protein 1 (CDCP1) is overexpressed in several
cancer types and is a predictor of poor prognosis for patients on standard of care
therapies. Phosphorylation of CDCP1
tyrosine sites is induced upon loss of cell adhesion and is thought to be linked to metastatic potential of
tumor cells. Using a
tyrosine-phosphoproteomics screening approach, we characterized the phosphorylation state of CDCP1 across a panel of
breast cancer cell lines. We focused on two phospho-
tyrosine pTyr
peptides of CDCP1, containing Tyr707 and Tyr806, which were identified in all six lines, with the human
epidermal growth factor 2-positive HCC1954 cells showing a particularly high phosphorylation level. Pharmacological modulation of
tyrosine phosphorylation indicated that, the
Src family kinases (SFKs) were found to phosphorylate CDCP1 at Tyr707 and Tyr806 and play a critical role in CDCP1 activity. We demonstrated that CDCP1 overexpression in HEK293 cells increases global
phosphotyrosine content, promotes anchorage-independent cell growth and activates several SFK members. Conversely, CDCP1 downregulation in multiple solid
cancer cell lines decreased both cell growth and SFK activation. Analysis of primary human
tumor samples demonstrated a correlation between CDCP1 expression, SFK and
protein kinase C (PKC) activity. Taken together, our results suggest that CDCP1 overexpression could be an interesting therapeutic target in multiple solid
cancers and a good
biomarker to stratify patients who could benefit from an anti-SFK-targeted
therapy. Our data also show that multiple
tyrosine phosphorylation sites of CDCP1 are important for the functional regulation of SFKs in several
tumor types.