c-Kit-dependent growth of uveal melanoma cells: a potential therapeutic target?
OBJECTIVE
This study was conducted to investigate the expression and functional impact of the proto-oncogene c-kit in uveal melanoma.


METHODS
Based on immunohistochemical (IHC) study of paraffin-embedded specimens from 134 uveal melanomas and Western blot analysis on eight fresh-frozen samples the expression of c-kit in uveal melanoma was studied. Furthermore, the phosphorylation of c-kit and the impact of the tyrosine kinase inhibitor STI571 was examined in the three uveal melanoma cell lines OCM-1, OCM-3, and 92-1.


RESULTS
Eighty-four of 134 paraffin-embedded samples and six of eight fresh-frozen samples expressed c-kit. c-Kit was strongly expressed and tyrosine phosphorylated in cultured uveal melanoma cells compared with cutaneous melanoma cells. Moreover, in contrast to cutaneous melanoma cell lines c-kit maintained a high phosphorylation level in serum-depleted uveal melanoma cells. No activation-related mutations in exon 11 of the KIT gene were found. On the contrary, expression of the stem cell growth factor (c-kit ligand) was detected in all three uveal melanoma cell lines, suggesting the presence of autocrine (paracrine) stimulation pathways. Treatment of uveal melanoma cell lines with STI571, which blocks c-kit autophosphorylation, resulted in cell death. The IC(50) of the inhibitory effects on c-kit phosphorylation and cell proliferation was of equal size and less than 2.5 microM.


CONCLUSIONS
The results confirm that c-kit is vastly expressed in uveal melanoma, suggest that the c-kit molecular pathway may be important in uveal melanoma growth, and point to its use as a target for therapy with STI571.
All-Ericsson
Charlotta
C
St. Erik's Eye Hospital, Stockholm, Sweden.
Girnita
Leonard
L
Müller-Brunotte
Anja
A
Brodin
Bertha
B
Seregard
Stefan
S
Ostman
Arne
A
Larsson
Olle
O
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001549:Benzamides; D015153:Blotting, Western; D002455:Cell Division; D005260:Female; D006801:Humans; D000068877:Imatinib Mesylate; D007124:Immunoenzyme Techniques; D008297:Male; D008545:Melanoma / Q000378:metabolism* / Q000473:pathology*; D008875:Middle Aged; D016612:Paraffin Embedding; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines; D016133:Polymerase Chain Reaction; D000090063:Proto-Oncogene Mas; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D012878:Skin Neoplasms / Q000378:metabolism / Q000473:pathology; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism; D014604:Uveal Neoplasms / Q000378:metabolism* / Q000473:pathology*
D001549:Benzamides; C000715470:MAS1 protein, human; D010879:Piperazines; D000090063:Proto-Oncogene Mas; D011743:Pyrimidines; D012333:RNA, Messenger; D014443:Tyrosine; D000068877:Imatinib Mesylate; D019009:Proto-Oncogene Proteins c-kit