Insulin-like growth factors stimulate growth and L-cysteine uptake by the intestinal parasite Giardia lamblia.
Giardia lamblia, a parasitic protozoan responsible for diarrhea and malabsorption in humans, grows axenically only in media that contain serum and a high concentration of L-cysteine. During our attempts to grow Giardia in the absence of serum, we found that: (a) human insulin-like growth factors (especially IGF-II), but not insulin, promote the growth and L-cysteine uptake by G. lamblia trophozoites; (b) the growth stimulation was inhibited by alpha IR3, an anti-type 1 IGF receptor monoclonal antibody, but an anti-type 2 IGF receptor antibody had no effect; and (c) IGFs act on Giardia through a type 1 IGF receptor-like protein, which can bind IGF-II with higher affinity than IGF-I, and most likely possesses intrinsic phosphotyrosine kinase activity.
Luján
H D
HD
Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892.
Mowatt
M R
MR
Helman
L J
LJ
Nash
T E
TE
D000818:Animals; D016895:Culture Media, Serum-Free; D003545:Cysteine / Q000378:metabolism*; D016829:Giardia lamblia / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology*; D017451:Receptors, Somatomedin / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology
D016895:Culture Media, Serum-Free; D017451:Receptors, Somatomedin; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D003545:Cysteine