Immunohistochemical and in situ hybridization studies of androgen receptor expression in a transplantable androgen-independent prostatic carcinoma line (AIT) of Noble rats.
BACKGROUND
In a previous study, we had shown that testosterone (T) administration to castrated Noble (NBL) rats, bearing an androgen-independent prostatic carcinoma line (AIT), caused a dramatic increase in high-affinity nuclear-androgen binding sites in the neoplasms. This increase in nuclear androgen receptors (AR) was accompanied by a transient doubling of the mitotic index in the tumors.


METHODS
In our current study we used immunohistochemistry and in situ hybridization to investigate the effects of androgen withdrawal and replacement on AR expression at the molecular/cellular level in the AIT. Results from immunohistochemical studies of AR expression in the AIT were compared with those from the prostates of intact, castrated, and castrated T-treated rats.


RESULTS
Immunopositive staining for AR was found only in the nuclei of prostatic cells from the glands of intact, castrated or castrated T-treated animals. A few immunopositive tumor cells were present in AITs carried in untreated castrated hosts. In all instances, the reaction product was found in the cytoplasm, but it was also present in the nuclei of some tumor cells. Five days of T administration to castrated AIT-bearing rats caused a dramatic increase in immunopositive tumor cells. Nuclear staining was observed in all positive cells, but the reaction product was also present as well in the cytoplasm of some tumor cells. No differences in AR mRNA expression was detected by in situ hybridization studies of the AITs from castrated and castrated T-treated rats.


CONCLUSIONS
The differences in localization of AR between normal prostate and carcinoma cells may reflect alterations in DNA binding domains of the AR protein that occurred with neoplastic transformation. Our in situ findings suggest that unlike the normal prostate, where AR mRNA levels are autoregulated by androgen, AIT cells constitutively express these transcripts. Taken together, our findings suggest that the T-mediated increases in nuclear AR in the AIT, detected previously by binding assay and now by immunohistochemistry, are likely the result of post-transcriptional modifications in the receptor protein.
Leav
I
I
Department of Pathology, Tufts University School of Medicine, Boston, Massachusetts.
Kwan
P W
PW
Merk
F B
FB
Chang
C
C
Ho
S M
SM
D000818:Animals; D015972:Gene Expression Regulation, Neoplastic; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008297:Male; D009368:Neoplasm Transplantation; D011471:Prostatic Neoplasms / Q000737:chemistry* / Q000235:genetics / Q000473:pathology*; D012333:RNA, Messenger / Q000032:analysis; D012334:RNA, Neoplasm / Q000032:analysis; D051381:Rats; D011944:Receptors, Androgen / Q000032:analysis*; D014407:Tumor Cells, Cultured
D012333:RNA, Messenger; D012334:RNA, Neoplasm; D011944:Receptors, Androgen