A Distinctive Pattern of Different Gene Expression in Chronic Myelogenous Leukemia Patients

Introduction: Molecular chaperones have many functions, such as protecting other proteins against aggregation, assisting in folding of nascent proteins/refolding of damaged proteins and targeting severely damaged proteins to degradation. As one of the molecular chaperones, Hsp90 functions to facilitate the folding of newly synthesized and denatured client proteins, including mutated p53, Bcr-Abl, p185^ErbB2 and Raf-1. The Bcr-Abl fusion gene encodes for the p210^Bcr-Abl tyrosine kinase (TK) implicated in the pathogenesis of chronic myelogenous leukemia (CML). Studies in cultured cells have identified many signal transduction pathways activated by Bcr-Abl, including activation of the Ras, MAPK, JNK/SAPK, phosphatidylinositol-3 kinase, nuclear factor-B and STAT pathways. Imatinib mesylate (imatinib IM) is a tyrosine kinase inhibitor that competitively inhibits ATP binding in the kinase domains of both the Bcr-Abl and c-Abl kinases. It has been suggested that resistance to imatinib stems from Bcr-Abl gene amplification, leading to overexpression of Bcr-Abl protein or point mutations in the Bcr-Abl gene However, several groups suggested that there might be other forms of Bcr-Abl-independent imatinib resistance Recently, it has been reported that changes in histone deacetylase (HDAC) expression in leukemic cells could be involved in mechanisms for abnormal cellular proliferation that operate through chromatin-independent pathways and thereby could lead to acquired drug resistance of the cells

In the present study, we evaluated in primary leukemic blasts, obtained from chronic myelogenous leukemia patients at onset, patients in blast crisis and patients which were imatinib-resistant The espression the sirtuin members family and HSP70, HSP90 i-NOS and bcl-2 was evaluated by Nortern blot and Western blot analysis.

Material and Methods: Primary leukaemia blasts

We harvested primary blast rich mononuclear cells were obtained by gradient centrifugation on ficoll-hypaque of bone marrow and peripheral blood cells after obtaining appropriate informed consent.

Northern blot

Total RNAs from control or treated cells were isolated using Tri Reagent Aliquots of RNA were electrophoresed and blotted onto nylon membranes, that hybridized to ³²P-labelled probe.

Western Blot

Cells were lysed and. then were centrifugated. Protein concentration was determined by the Bradford assay.. Equivalent amounts of protein loaded and electrophoresed and were transferred to nitrocellulose membranes, that were incubated with the different primary antibodies:,

Result and Discussion:. In the present study, we evaluated a pattern of different gene expression by Northern Blot and Western Blot analysis in bone marrow and peripheral blood cells from 16 CML patients at onset, from 2 patients in blast crisis evolved under IM treatment, and 14 imatinib-resistant patients. Some RNAs were underexpressed in most or all samples tested and never overexpressed (eg SIRT2, SIRT3, SIRT4 and SIRT5), while others were overexpressed in the great majority of samples and rarely, if ever, underexpressed (eg SIRT1, SIRT7, HSP90, iNOS)Furthermore, we examined the level of heat-shock related proteins HSP90 and bcl-2 in 2 patients during treatment with IM. and one patient IM-resistant by western Blot analysis: HSP90 and BCl-2 increased one patient during treatment with IM, while both protein levels was very high in one one patient IM-resistant These results suggest that the difference of genes expression might contribute to patterns of clinical response.