Prolactin receptor expression in the developing human prostate and in hyperplastic, dysplastic, and neoplastic lesions

Abstract

In situ hybridization and immunohistochemistry were used to localize and compare the expression of the long form of the human prolactin receptor in fetal, prepubertal, and adult prostate. Results were then compared with hyperplastic, dysplastic, and neoplastic lesions. Both receptor message and protein were predominately localized in epithelial cells of the fetal, neonatal, prepubertal, and normal adult prostate. In hyperplastic lesions the expression of the receptor was unchanged with respect to normal epithelial cells. Irrespective of grade, markedly enhanced expression of the receptor was evident in dysplastic lesions. In lower Gleason grade carcinomas the intensity of receptor signal at the message and protein levels approximated that found in normal prostatic epithelium. However, in foci within higher grade cancers, receptor expression appeared diminished. Results from our study suggest that prolactin action plays a role in the development and maintenance of the human prostate and may also participate in early neoplastic transformation of the gland. Diminution of receptor expression in high grade neoplasms could reflect the emergence of a population of cells that are no longer responsive to the peptide hormone.

Figure 1.

A and B: Fetal human prostate at 34 weeks of gestation. Cords of epithelial cells are found in solid nests or arranged around a lumen. A: In situ hybridization. Strong signals are uniformly evident in epithelial cells. In contrast only faint signals are present in stromal components (×250). B: Immunostaining of the same fetal gland illustrated in A with the CL-AB reagent. Light to moderate immunostaining is seen in the cytoplasm of basal and luminal cells. Compare the relatively light intensity of immunostaining with the strong hybridization signal present in epithelial cells in A. No immunostaining of stroma is observed in this field but in other areas and in other immature glands faint staining was occasionally detected with either antibody (×250). C–E: Normal adult prostate from the peripheral zone. C: In situ hybridization. Light to moderate signal is evident in the cytoplasm of epithelial cells. No signal is present in stromal cells in this field (×350). D and E: Immunohistochemical localization of PRLr using the CL-AB reagent in the peripheral zone from the same case illustrated in C. D: The cytoplasm of secretory cells are lightly stained. Basal cell nuclei appear to be moderately stained while those of secretory cells appear unstained. No staining of stromal cells is evident in this field (×250). E: In this higher power micrograph from the normal peripheral zone in a different case, immunostaining of nuclei of basal and secretory cells is evident (×600).

Figure 2.

A and B: Benign prostatic hyperplasia. A: In situ hybridization. The localization of PRLr message is almost exclusively present in hyperplastic epithelial cells within the nodule. The intensity of signal approximates that found in normal epithelium (×250). B: Immunohistochemical staining with the CL-AB reagent of the same lesion illustrated in A. As was the case for normal epithelial cells, staining intensity is light to moderate. Nuclear staining was infrequent in this example. Note the almost total absence of positivity in the stromal component of the nodule as detected by either in situ hybridization or immunohistochemistry (×220).

Figure 3.

A–G: Dysplasia. A: In situ hybridization. Note the intense signal present in the multiple foci of high grade dysplasia. An acinus that contains morphologically normal as well as dysplastic cells is present in the center of this field (×220). B: In situ hybridization. The differences between the intensity of receptor transcript expression in dysplastic (top) and normal (bottom) cells are well illustrated in these juxtaposed acini (×250). Also compare the intensity of signal in dysplastic lesions with that seen in normal epithelial cells in the lesion-free peripheral zone illustrated in Figure 1C ▶ . C: In situ hybridization of a high grade dysplastic lesion. This high magnification micrograph exemplifies the intense expression of PRLr message we consistently found in dysplastic lesions irrespective of their grade or anatomical location (×600). D: In situ hybridization using the sense probe of the dysplastic lesion illustrated in C. Note the total absence of hybridization in this lesion when the sense probe was used. The same negative results were obtained when the antisense probe was omitted (×350). Immunohistochemistry of moderate (E) and severe (F) grade dysplastic lesions using the CL-AB reagent (×400 for both panels). Note the intense cytoplasmic staining in both lesions. Interestingly, the nuclei of dysplastic epithelial cells are unstained. Compare with hybridization and immunohistochemical findings in normal and hyperplastic epithelial cells in Figures 1 and 2 ▶ ▶ . G: Competition control in a section of normal peripheral zone. Peptide and the CL-AB were preincubated before application to the section, as described under Materials and Methods; no staining is evident. The same results were obtained when the primary antibody was omitted.

Figure 4.

A–D: Carcinoma of the prostate. A and B: In situ hybridization, grade 3 carcinoma (A) and grade 4 carcinoma (B). The intensity of signal in the grade 3 carcinoma approximates that seen in normal prostate. The signal appears less intense in this grade 4 carcinoma when compared with its more well differentiated counterpart or the expression in normal prostate (×250). C and D: Immunohistochemistry using the CL-AB reagent. The results seen with immunostaining in grade 3 (C) and grade 4 (D) carcinomas approximates the level of intensity seen in these lesions by in situ hybridization.

Figure 5.

Immunoblot. The blot illustrates a single band of approximately 85–90 kd detected in lysates of MCF-7, LNCap, and PC-3 cells. Note the intense band detected in the MCF-7 cells and compare this with the less intense bands present in LNCaP and PC-3 cells, respectively. Molecular weight markers are illustrated on the left.