Regulation of eukaryotic translational initiation in transformed and differentiation inducible haemopoietic cell lines
2014-12-15T10:32:31Z (GMT) by
Mechanisms which regulate gene expression at the level of protein synthesis play an important role in the control of cell proliferation, and de-regulation of translation has been shown to cause cell transformation. Haemopoiesis is a complex and highly regulated process of cell proliferation, differentiation and apoptosis which is subject to a variety of neoplastic disorders. Control of translation is usually effected through modulation of the eukaryotic initiation factors (eIFs) and cultured cells of haemopoietic origin were chosen to study eIFs and their regulation.;The eIFs were examined in cell lines derived from patients with the B-cell tumours Burkitt's lymphoma and Multiple Myeloma. Study of the expression of the proto-oncogene c-myc and its transcriptional targets, eIF4E and eIF2 demonstrated no correlation between the eIFs and c-myc expression. Investigation of another component of the eIF4F complex revealed that eIF4G is cleaved into specific N- and C-terminal fragments in the Multiple Myeloma cell line GM2132. This suggests that in these cells there may be an advantage for mRNAs translated by internal ribosome entry.;HL60, a differentiation inducible leukaemic cell line, was used to investigate alterations in protein synthesis during granulocytic differentiation. A 2-fold increase in eIF4E phosphorylation was observed which does not affect the protein synthesis rate. This implies that the increase in eIF4F phosphorylation may specifically affect the translation of a sub-set of mRNAs. Differentiating HL60 cells were also used to study the relationship between c-myc, eIF4E and eIF2 expression. No correlation between expression of c-myc and eIF4E was found in this system. However, eIF2 expression did appear to be responsive to c-Myc during the initial stages of granulocytic differentiation.;Investigation of a serum response in HL60 cells demonstrated that association of eIF4G with eIF4E is modulated by alterations in eIF4G protein levels. This suggests that eIF4E is not a limiting factor in the initiation of translation in HL60 cells.