IGF-1R tyrosine kinase expression and dependency in clones of IGF-1R knockout cells (R-).
Insulin-like growth factor 1 receptor (IGF-1R) plays many crucial roles in cancer, like anti-apoptotic activity and necessity for transformation. IGF-1R knockout cells (R-) represent a useful tool for molecular mapping of biological properties of the receptor. R- cells have been shown to be refractory to transformation by viral and cellular oncogenes, highlighting the necessity of this receptor for transformation. Surprisingly, more recent studies have shown that these cells can undergo spontaneous transformation. This observation raises the question as whether R- cells over the years have acquired some properties mimicking those of IGF-1R. Using an IGF-1R inhibitor (cyclolignan PPP) we have identified clones of R- (R-s) that are sensitive to this compound. Since, PPP is closely related to podophyllotoxin, which is an efficient microtubule inhibitor, we first investigated if such a mechanism could explain the sensitivity to PPP. However, highly purified PPP showed no or very slight tubulin binding. Further analysis of R-s revealed expression of a 90 kDa protein being reactive to IGF-1R beta-subunit antibodies. This protein was weakly but constitutively tyrosine phosphorylated and was downregulated by siRNA targeting IGF-1R. This downregulation was paralleled by decreased R-s survival. Taken together, our study suggests that clones of R- express IGF-1R activity and dependency, which in turn may explain that R- can undergo spontaneous transformation.
Rosengren
Linda
L
Department of Oncology and Pathology, Division of Cellular and Molecular Tumor Pathology, CCK, R8:04, Karolinska University Hospital Solna, SE-171 76 Stockholm, Sweden.
Vasilcanu
Daiana
D
Vasilcanu
Radu
R
Fickenscher
Sandra
S
Sehat
Bita
B
Natalishvili
Nathalia
N
Naughton
Sean
S
Yin
Shucheng
S
Girnita
Ada
A
Girnita
Leonard
L
Axelson
Magnus
M
Larsson
Olle
O
D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D015536:Down-Regulation; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D011034:Podophyllotoxin / Q000031:analogs & derivatives / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics*; D014404:Tubulin / Q000378:metabolism; D014407:Tumor Cells, Cultured
D034741:RNA, Small Interfering; D014404:Tubulin; C415032:picropodophyllin; D017526:Receptor, IGF Type 1; D011034:Podophyllotoxin