CTLA4 associates with the SH2 domain containing tyrosine phosphatase SHP2 and this interaction is mediated through the YVKM motif of CTLA-4. Phosphorylation of tyrosine in the YVKM motif recruits SHP-2. Still the association of SHP-2 with CTLA-4 is unclear and remains controversial. Several other studies have reported that CTLA-4 does not directly associate with SHP-2. The interaction between the phosphatase and CTLA-4 may be an indirect event, possibly mediated by PI3-kinase/SHP-2 binding.