▁especially ▁for ▁cancer ▁th era pe ut ics . ▁In ▁recent ▁years , ▁A X L ▁has ▁emer ged ▁as ▁a ▁key ▁facil it ator ▁of ▁imm une ▁escape ▁and ▁drug - res istance ▁by ▁cancer ▁cells , ▁leading ▁to ▁ag gress ive ▁and ▁met ast atic ▁can cers . ▁ ▁A X L ▁is ▁a ▁cell ▁surface ▁re ceptor ▁ty ros ine ▁kin ase , ▁part ▁of ▁the ▁T AM ▁family ▁of ▁kin ases ▁including ▁T Y RO 3 ▁and ▁M ERT K . ▁ ▁Gene ▁and ▁protein ▁structure ▁ ▁The ▁A xl ▁gene ▁is ▁evolution arily ▁conser ved ▁between ▁verte br ate ▁species . ▁This ▁gene ▁has ▁two ▁different ▁altern atively ▁sp lic ed ▁trans cript ▁variants . ▁ ▁The ▁protein ▁encoded ▁by ▁this ▁gene ▁is ▁a ▁member ▁of ▁the ▁re ceptor ▁ty ros ine ▁kin ase ▁sub family . ▁Although ▁it ▁is ▁similar ▁to ▁other ▁re ceptor ▁ty ros ine ▁kin ases , ▁the ▁A xl ▁protein ▁represents ▁a ▁unique ▁structure ▁of ▁the ▁ext rac ell ular ▁region ▁that ▁ju xt ap oses ▁Ig L ▁and ▁F N III ▁repe ats . ▁ ▁The ▁A X L ▁protein ▁is ▁character ized ▁by ▁an ▁ext rac ell ular ▁structure ▁consisting ▁of ▁two ▁fib ron ect in ▁type ▁ 3 - like ▁repe ats ▁and ▁two ▁imm un og lob ul in - like ▁repe ats ▁along ▁with ▁its ▁int rac ell ular ▁ty ros ine ▁kin ase ▁domain . ▁ ▁A X L ▁is ▁in ▁close ▁vic inity ▁to ▁the ▁B