Rabbit polyclonal antibody to Raf~1 (S621)

A~Raf, B~Raf, and c~Raf (Raf~1) are the main effectors recruited by GTP~bound Ras to activate the MEK~MAP kinase pathway. Activation of c~Raf is the best understood and involves phosphorylation at multiple activating sites, including Ser338, Tyr341, Thr491, Ser494, Ser497, and Ser499. p21~activated kinase (PAK) has been shown to phosphorylate c~Raf at Ser338, and the Src family phosphorylates Tyr341 to induce c~Raf activity. Ser338 of c~Raf corresponds to similar sites in A~Raf (Ser299) and B~Raf (Ser445), although this site is constitutively phosphorylated in B~Raf. Inhibitory 14~3~3 binding sites on c~Raf (Ser259 and Ser621) can be phosphorylated by Akt and AMPK, respectively. While A~Raf, B~Raf, and c~Raf are similar in sequence and function, differential regulation has been observed. Of particular interest, B~Raf contains three consensus Akt phosphorylation sites (Ser364, Ser428, and Thr439) and lacks a site equivalent to Tyr341 of c~Raf. Research studies have shown that the B~Raf mutation V600E results in elevated kinase activity and is commonly found in malignant melanoma. Six residues of c~Raf (Ser29, Ser43, Ser289, Ser296, Ser301, and Ser642) become hyperphosphorylated in a manner consistent with c~Raf inactivation. The hyperphosphorylation of these six sites is dependent on downstream MEK signaling and renders c~Raf unresponsive to subsequent activation events.