An anti-Ras cancer potential of PP1, an inhibitor specific for Src family kinases: in vitro and in vivo studies.
BACKGROUND
We previously found that both PAK, a Rac/CDC42-activated Ser/Thr kinase, and its binding partner PIX are required for malignant transformation caused by oncogenic Ras mutants, such as v-Ha-Ras. Furthermore, oncogenic Ras requires an autocrine pathway to activate PAK. This pathway involves at least two distinct receptor kinases: EGF receptor (ErbB1) and ErbB2. Interestingly, both of these kinases are known to activate Src family kinases that phosphorylate CAT, another binding partner of PIX.


OBJECTIVE
The major aim of this study was to determine whether Src family kinases are required for both Ras-induced PAK activation and malignant transformation. For this purpose, we used PP1, an inhibitor specific for Src family kinases, which does not inhibit either EGF receptor or ErbB2.


RESULTS
We studied the effect of PP1 on the anchorage-dependent growth of normal and v-Ha-Ras transformed NIH 3T3 fibroblasts, PAK activation and anchorage-independent growth of Ras transformants, and development of Ras-induced sarcomas in nude mice. We found that PP1 (10 nM) strongly inhibits PAK activity in Ras transformants. PP1 at this concentration is known to inhibit c-Fyn kinase, but not c-Src kinase, and none of the three known Src family kinases (c-Src, c-Fyn, and c-Yes) expressed in fibroblasts is activated by v-Ha-Ras. Thus, it is most likely that the primary target of this drug is an as yet unidentified Ras-activated Tyr (Y) kinase or kinases, which we call "Ray." Although PP1 has no effect on their anchorage-dependent growth, it significantly inhibits their anchorage-independent growth in soft agar, as well as a rapid growth of Ras-induced sarcomas in mice.


CONCLUSIONS
Like EGF receptor and ErbB2, a member of Src family kinases (most likely a new Src-related kinase called "Ray") is essential for the Ras-induced activation of PAK and the malignant transformation both in vitro and in vivo. These findings suggest that PP1 and other inhibitors specific for Src family kinases are potentially useful for the treatment of Ras-associated cancers.
He
H
H
Ludwig Institute for Cancer Research, Melbourne, Australia.
Hirokawa
Y
Y
Levitzki
A
A
Maruta
H
H
D016475:3T3 Cells; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D002455:Cell Division / Q000187:drug effects; D002461:Cell Line, Transformed; D004789:Enzyme Activation; D005260:Female; D051379:Mice; D008819:Mice, Nude; D015689:Oncogene Protein p21(ras) / Q000037:antagonists & inhibitors*; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011720:Pyrazoles / Q000494:pharmacology / Q000627:therapeutic use*; D011743:Pyrimidines / Q000494:pharmacology / Q000627:therapeutic use*; D012509:Sarcoma / Q000188:drug therapy*; D015398:Signal Transduction; D054462:p21-Activated Kinases; D019061:src-Family Kinases / Q000037:antagonists & inhibitors* / Q000502:physiology
C108123:4-amino-5-(4-methylphenyl)-7-(tert-butyl)pyrazolo(3,4-d)pyrimidine; D000970:Antineoplastic Agents; D020033:Protein Isoforms; D011720:Pyrazoles; D011743:Pyrimidines; D019061:src-Family Kinases; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D015689:Oncogene Protein p21(ras)