Depletion of intracellular Ca2+ stores, phosphorylation of eIF2alpha, and sustained inhibition of translation initiation mediate the anticancer effects of clotrimazole

PKR, apoptosis and cancer

The double-stranded (ds) RNA-regulated serine/threonine protein kinase, PKR, is an interferon-inducible enzyme of widespread occurrence in mammalian cells. PKR is activated by dsRNA via a mechanism involving autophosphorylation. Once activated, the enzyme phosphorylates the alpha-subunit of protein synthesis initiation factor eIF2, thereby inhibiting translation. Accumulating data suggest that PKR has additional substrates, and that the kinase may also regulate gene transcription and signal transduction pathways. Although PKR plays an important role in mediating the antiviral effects of interferons, PKR is also implicated in regulating cell proliferation in uninfected cells and may have a tumor suppressor function under normal conditions. Studies of human malignancies and tumor cell lines suggest that, in general, patients bearing tumors with a higher PKR content have a more favorable prognosis. However, in human breast carcinoma cells, dysregulation of PKR may be associated with the establishment or maintenance of the transformed state.

Translational control: the cancer connection

There is now a growing body of evidence which suggests links between the regulation of protein synthesis and the disruption of cell behaviour that typifies cancer. This directed issue of the International Journal of Biochemistry and Cell Biology presents several review articles of relevance to this field. The topics covered include the significance of the regulation and overexpression of polypeptide chain initiation factors for cell transformation and malignancy, the role of mRNA structure in the control of synthesis of key growth regulatory proteins, the actions of the eIF2 alpha-specific protein kinase PKR in the control cell growth and apoptosis, and the involvement of the elongation factor eEF1 in oncogenesis. The purpose of this article is to give an overview of the field and to indicate where we may expect developments to occur in the next few years.