Suppression of c-myc is a critical step in glucocorticoid-induced human leukemic cell lysis.

R Thulasi,D.V Harbour,E.B Thompson

doi:10.1016/s0021-9258(17)46845-1

R Thulasi, D.V Harbour + Show 1 more

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https://doi.org/10.1016/s0021-9258(17)46845-1

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Abstract

Glucocorticoids evoke cytolysis in clonal human leukemic CEM-C7 cells. Suppression of c-myc mRNA by dexamethasone closely correlates with cell lysis only in CEM clones with both glucocorticoid receptor and intact lysis functions. We tested the theory that c-myc repression is essential for glucocorticoid-induced lymphocytolysis by preventing down-regulation of c-myc gene in the presence of dexamethasone and by reducing c-myc mRNA levels with antisense oligonucleotides. We find that sustained expression of c-myc provides resistance to dexamethasone-induced lysis, and antisense c-myc oligomers induce cell lysis. The lethal effects of dexamethasone in these leukemic cells appear to involve reduction of c-myc below the levels required to maintain cellular growth and integrity.

Highlights

The ho- is a glucocorticoid-sensitive clonal line obtained from parental loglucocorticoid receptor is necessary, but not sufficient, to in- CCRF-CEM cells
CEM-C7 cells transfected with the metallothionein I c-myc (MTmyc) expression vector were treated with Zn2+only, Zn2+ plus Dex (1PM),or ethanol vehicle, and viable cell numbers were determined at intervals
Incubation of CEM-C7 Cells with Antisense Oligomers Induces Cell Lysis and Reduces Myc Protein Levels-The second Normal cell growth and proliferation are regulatedby a baltest of the central role ofc-myc in maintaining CEM-C7 cell ance between growth-promoting and growth-suppressing facviability was todown-regulate the c-myc gene by non-steroidal tors, which are the products of growth-regulating genes

Summary

EXPERIMENTAL PROCEDURES

Frozen cell pellets were solubitransfectedwith: ( a ) no DNA, (b) pBR322, or (c) pSVzneo, plasmid lized in 100 pl of cold antibody buffer In all these instances, tnhoenspecific lysis 0.5% Nonidet P-40, 0.5% deoxycholate, 0.5% SDS, and 10mM iodoaceobserved was less than 4%. Steroid Deatment andCell Viability-Twenty-four h after transfec- body raised against recombinantMyc protein R3586 overnight a t 4 "C. tion, cells were resuspended to about 2 x 105/ml in fresh RPMI 1640 Thanetigen-antibody complex wparsecipitatewdipthrotein containing 5% FBS. Antibody Preparations-A hybridoma cell line CRL1729, secreting a monoclonal antibody MYC 1-9E10.2 [35], raised against a synthetic

RESULTS

DISCUSSION

Findings

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