Tyrosine phosphorylation regulates maturation of receptor tyrosine kinases.
Constitutive activation of receptor tyrosine kinases (RTKs) is a frequent event in human cancer cells. Activating mutations in Fms-like tyrosine kinase 3 (FLT-3), notably, internal tandem duplications in the juxtamembrane domain (FLT-3 ITD), have been causally linked to acute myeloid leukemia. As we describe here, FLT-3 ITD exists predominantly in an immature, underglycosylated 130-kDa form, whereas wild-type FLT-3 is expressed predominantly as a mature, complex glycosylated 150-kDa molecule. Endogenous FLT-3 ITD, but little wild-type FLT-3, is detectable in the endoplasmic reticulum (ER) compartment. Conversely, cell surface expression of FLT-3 ITD is less efficient than that of wild-type FLT-3. Inhibition of FLT-3 ITD kinase by small molecules, inactivating point mutations, or coexpression with the protein-tyrosine phosphatases (PTPs) SHP-1, PTP1B, and PTP-PEST but not RPTPalpha promotes complex glycosylation and surface localization. However, PTP coexpression has no effect on the maturation of a surface glycoprotein of vesicular stomatitis virus. The maturation of wild-type FLT-3 is impaired by general PTP inhibition or by suppression of endogenous PTP1B. Enhanced complex formation of FLT-3 ITD with the ER-resident chaperone calnexin indicates that its retention in the ER is related to inefficient folding. The regulation of RTK maturation by tyrosine phosphorylation was observed with other RTKs as well, defines a possible role for ER-resident PTPs, and may be related to the altered signaling quality of constitutively active, transforming RTK mutants.
Schmidt-Arras
Dirk-E
DE
Institute of Molecular Cell Biology, Medical Faculty, Friedrich Schiller University, Drackendorfer Strasse 1, D-07747 Jena, Germany.
Böhmer
Annette
A
Markova
Boyka
B
Choudhary
Chunaram
C
Serve
Hubert
H
Böhmer
Frank-D
FD
D000818:Animals; D037281:Calnexin / Q000502:physiology; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D010766:Phosphorylation; D017510:Protein Folding; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D020794:Receptor Protein-Tyrosine Kinases / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism*; D051941:fms-Like Tyrosine Kinase 3
D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D037281:Calnexin; D014443:Tyrosine; C497970:FLT3 protein, human; D020794:Receptor Protein-Tyrosine Kinases; D051941:fms-Like Tyrosine Kinase 3; D017027:Protein Tyrosine Phosphatases