PTK6 (BRK) phosphorylates CBL at tyrosine residues Y700, Y731 and Y774, which are also targeted by other SRC family kinases. It has not been examined whether CBL and PTK6 interact directly. However, it has been shown that CBL expression is reciprocal (inversely related) to PTK6 in several cancer cell lines (Pires et al. 2014). CBL is an E3 ubiquitin ligase that negatively regulates EGFR, targeting it for degradation (Kang and Lee 2013). CBL is also implicated as a putative E3 ubiquitin ligase for PTK6 in normoxia (Pires et al. 2014).