PKCalpha activation downregulates ATM and radio-sensitizes androgen-sensitive human prostate cancer cells in vitro and in vivo.
We previously demonstrated that treatment of human androgen-responsive prostate cancer cell lines LNCaP and CWR22-Rv1 with 12-O-tetradecanoylphorbol 13-acetate (TPA), a known protein kinase C (PKC) activator, decreases ATM protein levels, thus de-repressing the enzyme ceramide synthase (CS) and promoting apoptosis as well as radio-sensitizing these cells.(1) Here we show that PKCalpha mediates the TPA effect on ATM expression, since ATM suppression and apoptosis induced by either TPA or diacylglycerol-lactone (DAG-lactone), both inducing PKCalpha activation,(2) are abrogated in LNCaP cells following transfection of a kinase-dead PKCalpha mutant (KD-PKCalpha). Similarly, KD-PKCalpha blocks the apoptotic response elicited by combination of TPA and radiation, whereas expression of constitutively active PKCalpha is sufficient to sensitize cells to radiation alone, without a need to pre-treat the cells with TPA. These findings identify CS activation as a downstream event of PKCalpha activity in LNCaP cells. Similar results were obtained in CWR22-Rv1 cells with DAG-lactone treatment. Using the LNCaP orthotopic prostate model it is shown that treatment with TPA or DAG-lactone induces significant reduction in tumor ATM levels coupled with tumor growth delay. Furthermore, while fractionated radiation alone produces significant tumor growth delay, pretreatment with TPA or DAG-lactone significantly potentiates tumor cure. These findings support a model in which activation of PKCalpha downregulates ATM, thus relieving CS repression by ATM and enhancing apoptosis via ceramide generation. This model may provide a basis for the design of new therapies in prostate cancer.
Truman
Jean-Philip
JP
Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, Frederick, Maryland, USA.
Rotenberg
Susan A
SA
Kang
Ji-Hye
JH
Lerman
Gabriel
G
Fuks
Zvi
Z
Kolesnick
Richard
R
Marquez
Victor E
VE
Haimovitz-Friedman
Adriana
A
D015107:4-Butyrolactone / Q000031:analogs & derivatives / Q000494:pharmacology; D000728:Androgens / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D007700:Kinetics; D008297:Male; D011471:Prostatic Neoplasms / Q000201:enzymology / Q000473:pathology*; D051571:Protein Kinase C-alpha / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism; D014631:Valerates / Q000494:pharmacology
C406230:(1-(hydroxymethyl)-4-(4-methyl-3-(methylethyl)pentylidene)-3-oxo-2-oxolanyl)methyl 4-methyl-3-(methylethyl)pentanoate; D000728:Androgens; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D025521:Tumor Suppressor Proteins; D014631:Valerates; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D051571:Protein Kinase C-alpha; D013755:Tetradecanoylphorbol Acetate; D015107:4-Butyrolactone