Expression of the Double-Stranded RNA-Dependent Protein Kinase (p68) in Human Breast Tissues

Abstract

P68 is a potent inhibitor of protein synthesis in virally infected cells and has been suggested to function in noninfected cells as a tumor suppressor gene. We have previously demonstrated that p68 expression correlates directly with cellular differentiation and inversely with proliferative activity in normal epithelium and in several human tumor systems. In order to determine the role of p68 in human breast cancer, we utilized immunohistochemistry and mapped the expression of p68 in tissue from 200 breast biopsy specimens. A total of 434 foci, ranging from normal breast tissue to infiltrating carcinoma were examined. We found that p68 was present at basal levels in normal lobular and luminal ductal epithelial cells, with higher levels present in myoepithelial cells. Nonproliferative fibrocystic lesions showed variable expression of p68, with high levels seen within foci of apocrine metaplasia and low levels in cystically dilated terminal duct units. Low levels of p68 were seen in typical ductal proliferations, lobular neoplasia (atypical lobular hyperplasia and lobular carcinoma in situ), and in fibroadenomas. Foci of atypical ductal hyperplasia in situ and invasive ductal carcinoma generally showed higher levels of p68 expression. Among the infiltrating carcinomas, p68 expression correlated with nuclear grade. This suggests that the ability of p68 to inhibit cellular proliferation may be impaired in breast cancer and that its expression, although modestly paralleling cellular differentiation, is not a predictive indicator of improved survival.

Human breast cancer cells contain elevated levels and activity of the protein kinase, PKR

“…The chromagen staining in the carcinoma cells is blocked by PKR protein indicating that the staining is speci®c for PKR (data not shown). These results indicate that PKR expression in the breast carcinoma and the nontransformed cell lines are indeed similar to that reported in the carcinoma and the normal epithelial tissues from patients (Haines et al, 1996). We therefore proceeded to use the cell lines for biochemical analysis of the role of PKR in breast cancer.…”

“…An earlier immunohistochemical analysis of breast cancer tissues had indicated that PKR was expressed at high levels in carcinoma tissues as compared to the normal mammary ductal epithelial cells (Haines et al, 1996). To determine whether similar results pertain in cell lines, we performed immunohistochemical analysis on the cell lines derived from breast carcinoma and nontransformed cells.…”

“…The observation that PKR levels in head and neck squamous carcinomas are inversely proportional to that of PCNA, may lend support to PKR being anti-proliferative (Haines et al, 1998). On the other hand, PKR levels in human breast cancer tissues are several fold higher than in the surrounding normal epithelial cells (Haines et al, 1996). Lymphocytes derived from human leukemic patients have levels of PKR comparable to those derived from normal control individuals (Basu et al, 1997).…”

Doxorubicin bypasses the cytoprotective effects of eIF2α phosphorylation and promotes PKR-mediated cell death

“…For example, it was previously shown that human invasive ductal breast carcinomas and several human breast tumor cell lines contain elevated levels of PKR compared with non-malignant breast cells. 30,31 However, the PKR-eIF2a phosphorylation SubG1: 64% SubG1: 44% Figure 4 Phosphorylation of eIF2a protects cells from doxorubicin-induced death. (a) eIF2a S/S and eIF2a A/A MEFs were left untreated (con) or treated with 1 mM doxorubicin (dox) for the indicated time periods.…”

PKR; a sentinel kinase for cellular stress

“…In IL3-dependent cells the withdrawal of IL3 results in the phosphorylation of RAX, a protein activator of PKR and subsequent eIF2a phosphorlyation, inhibition of protein synthesis and apoptosis di erent human tumors and tumor cell lines (Haines et al, 1996;Zhou et al, 1998;Shimanda et al, 1998). Human invasive ductal breast carcinomas have high levels of PKR and in several breast carcinoma cell lines PKR levels are high compared to those found in lines derived from normal breast (Haines et al, 1996;Savinova et al, 1999). Despite high levels, the activity of PKR from the carcinoma cells is attenuated although it remains capable of binding dsRNA.…”