Loss of PKR activity in chronic lymphocytic leukemia

Abstract

There are a number of observations that suggest the dsRNA-activated protein kinase, PKR, may play an active role in formation and maintenance of leukemia, including nonrandom chromosomal deletions in acute leukemia as well as truncations and deletions of the PKR gene in some leukemia cell lines. However, there is little direct evidence from patient material that this is so. Here we show that full-length PKR is present but not active in 21 of 28 patient samples from B-cell chronic lymphocytic leukemia (B-CLL). PKR from these patients was unable to auto-activate or phosphorylate substrates but was able to bind dsRNA. Furthermore, the lack of PKR activation was not due to differing levels of the PKR activator, PACT nor of the PKR inhibitor, p58 IPK . We compared PKR status with clinical parameters and disease staging. No differences were found between the 2 groups in terms of staging (modified Rai or Binet), age, CD38 status, p53 status, 11q23 deletion status or CEP12 deletion status. However, there was a significant correlation between deletion in 13q14.3 and lack of PKR activity. We show that B-CLL cells appear to contain a soluble inhibitor of PKR, as lysates from cells lacking PKR activity were able to inhibit exogenous PKR in mixing experiments. Finally, we show suppression of PKR activity was still present following ultrafilitration through a 10,000 Da cutoff filter but was lost upon extraction with phenol/chloroform or by high salt washing. This data suggests loss of PKR activity may contribute to the formation and/or maintenance of CLL.

Impact of Protein Kinase PKR in Cell Biology: from Antiviral to Antiproliferative Action

“…Furthermore, a number of human leukemias and myelodysplasias have reduced PKR expression levels (21). A recent study with patients with chronic lymphocyte leukemia (B-CLL) showed that of 28 patient samples examined, 21 had no PKR activity despite the presence of a full-length protein; PKR from these patients could not be activated or phosphorylate substrates (154). It should be determined whether these cells have increased levels of some PKR inhibitor.…”

VSV-tumor selective replication and protein translation

“…PKR has been reported as being nonfunctional in tumors such as chronic lymphocytic leukemia and dominant-negative variants of PKR can transform immortalized murine cells (Koromilas et al, 1992;Meurs et al, 1993;Hii et al, 2004). Nevertheless, some evidence also indicates that PKR is not necessarily defective in a variety of other tumor cell types analysed and in some cases PKR has been reported as being overexpressed (Kim et al, 2002).…”

Dual induction of PKR with E2F-1 and IFN-α to enhance gene therapy against hepatocellular carcinoma

“…13 In those PKR downregulated tumors, which are often virally induced (like in HCC), the virus-mediated PKR inhibition could be counteracted by the therapeutic effect of E2F-1 in combination with PKR modifiers. 33 Our findings demonstrate, that PKR modification by agents, that are clinically already in use, is an attractive and effective strategy to enhance E2F-1 gene therapy against cancer.…”

“…Its low expression correlates with worse prognosis and enhanced tumorigenicity, suggesting that activated PKR has a tumor-suppressor function. 13 Inhibitors of heat-shock protein (HSP)-90 such as 17-allylamino-17-demethoxygeldanamycin (17-AAG) and radicicol have gained recent attention due to their antitumoral function and selective activity in malignant cells. These agents, which are currently being tested in phase I clinical trials, are also activators of PKR.…”