Zc. Zhang et al., GROWTH-DEPENDENT AND PKC-MEDIATED TRANSLATIONAL REGULATION OF THE UPSTREAM STIMULATING FACTOR-II (USF2) MESSENGER-RNA IN HEMATOPOIETIC-CELLS, Oncogene, 16(6), 1998, pp. 763-769
Upstream stimulating factor (USF2) is a basic helix-loop-helix leucine
zipper transcription factor, which is found in most tissues, A critic
al role for USF2 in cellular proliferation has been proposed based on
its importance in the regulation of various cyclins and P53 and its ca
pability to antagonize c-myc., In this paper we report that IL-3, whic
h is a major growth factor for mast cells, induces USF2 protein synthe
sis in murine mast cells (MC-9), Surprisingly, it does not significant
ly affect the level of USF2 mRNA in these cells at any of the time poi
nts tested, Using polysomal fractionation and RNA analysis we then dem
onstrated that this translational regulation is mostly the result of i
ncreased USF2 translational efficiency. Moreover, protein kinase C (PK
C) inhibitors prevented both the induction of USF2 protein synthesis a
nd the increase in USF2 translational efficiency in IL-3-activated mas
t cells, Two other hematopoietic cell lines were used to determine whe
ther the translational regulation of USF2 is of a more general nature:
mouse lymphosarcoma cells whose proliferation is inhibited by dexamet
hasone; and mouse erythroleukemia cells that differentiate upon exposu
re to hexamethylen bisacetamide, In both cell types, USF2 translation
was repressed in the non-dividing cells, This strongly implies that US
F2 is translationally repressed in quiescent hematopoietic cells, Cons
idering the proposed role of USF in proliferation it seems that transl
ational regulation of USF2 might have an important role in cellular gr
owth.