Stable expression of constitutively-activated STAT3 in benign prostatic epithelial cells changes their phenotype to that resembling malignant cells.
BACKGROUND
Signal transducers and activators of transcription (STATs) are involved in growth regulation of cells. They are usually activated by phosphorylation at specific tyrosine residues. In neoplastic cells, constitutive activation of STATs accompanies growth dysregulation and resistance to apoptosis through changes in gene expression, such as enhanced anti-apoptotic gene expression or reduced pro-apoptotic gene expression. Activated STAT3 is thought to play an important role in prostate cancer (PCA) progression. Because we are interested in how persistently-activated STAT3 changes the cellular phenotype to a malignant one in prostate cancer, we used expression vectors containing a gene for constitutively-activated STAT3, called S3c, into NRP-152 rat and BPH-1 human benign prostatic epithelial cells.


RESULTS
We observed that prostatic cell lines stably expressing S3c required STAT3 expression for survival, because they became sensitive to antisense oligonucleotide for STAT3. However, S3c-transfected cells were not sensitive to the effects of JAK inhibitors, meaning that STAT3 was constitutively-activated in these transfected cell lines. NRP-152 prostatic epithelial cells lost the requirement for exogenous growth factors. Furthermore, we observed that NRP-152 expressing S3c had enhanced mRNA levels of retinoic acid receptor (RAR)-alpha, reduced mRNA levels of RAR-beta and -gamma, while BPH-1 cells transfected with S3c became insensitive to the effects of androgen, and also to the effects of a testosterone antagonist. Both S3c-transfected cell lines grew in soft agar after stable transfection with S3c, however neither S3c-transfected cell line was tumorigenic in severe-combined immunodeficient mice.


CONCLUSIONS
We conclude, based on our findings, that persistently-activated STAT3 is an important molecular marker of prostate cancer, which develops in formerly benign prostate cells and changes their phenotype to one more closely resembling transformed prostate cells. That the S3c-transfected cell lines require the continued expression of S3c demonstrates that a significant phenotypic change occurred in the cells. These conclusions are based on our data with respect to loss of growth factor requirement, loss of androgen response, gain of growth in soft agar, and changes in RAR subunit expression, all of which are consistent with a malignant phenotype in prostate cancer. However, an additional genetic change may be required for S3c-transfected prostate cells to become tumorigenic.
Huang
Hosea F
HF
Division of Urology, Department of Surgery, UMDNJ-New Jersey Medical School,185 S, Orange, Ave,, Newark 07103, USA. huanghf@umdnj.edu <huanghf@umdnj.edu>
Murphy
Thomas F
TF
Shu
Ping
P
Barton
Arnold B
AB
Barton
Beverly E
BE
D000728:Androgens / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation; D002470:Cell Survival; D002471:Cell Transformation, Neoplastic; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D013196:Dihydrotestosterone / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology; D015870:Gene Expression; D006133:Growth Substances / Q000502:physiology; D006801:Humans; D053614:Janus Kinase 2; D008297:Male; D009154:Mutation; D010641:Phenotype; D011467:Prostate / Q000166:cytology; D011470:Prostatic Hyperplasia / Q000378:metabolism* / Q000473:pathology; D011471:Prostatic Neoplasms / Q000209:etiology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism; D050796:STAT3 Transcription Factor; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D020032:Tyrphostins / Q000494:pharmacology
D000728:Androgens; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D006133:Growth Substances; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D018168:Receptors, Retinoic Acid; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C494088:Stat3 protein, rat; D015534:Trans-Activators; D020032:Tyrphostins; C095512:alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide; D013196:Dihydrotestosterone; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507927:Jak2 protein, rat; D053614:Janus Kinase 2