MUCH1-XBP1 crosstalk in multiple myeloma
Date of Award
Doctor of Philosophy in Health Science (PhD)
Biological and Biomedical Sciences
Multiple myeloma (MM) is an incurable plasma cell (PC) neoplasm. Disease progression and treatment relapse is attributed to complex molecular pathway networks and to MM cancer stern cells (CSCs). Mucin 1 (MUC1) is a multi-functional glycoprotein. It has been shown to play a role in normal cellular biology of epithelial and lymphoid cells and in Tumour biology. There has been renewed interest in exploring the biological function of MUC1 and its association with drug resistance and CSC like phenotype in MM and other malignancies. X-box binding protein 1 (XBP1) is a transcription factor which plays a seminal role in differentiation of embryonic hepatocytes, pancreatic acinar cells and plasma cells. Knock down of XBP1 in MM has been associated with increased sensitivity to bortezomib and 17-AAG. The prognostic value and association of MUC1 and XBP1 in MM has not been reported before. Immortalized and or transformed cell lines play a major role in dissecting molecular pathways involved in the pathogenesis of disease. Ethnicity has been shown to be important in epidemiology, pathogenesis and response to treatment. Most cell lines used in cancer research and especially MM research are derived from a Caucasian population. One of the aims of this thesis was to establish MM cell lines from Pakistan. Establishment of primary cultures from 25 MM samples (bone marrow aspirates and peripheral blood) was undertaken which resulted in establishment of one cell line AKU-MYO1 (4% success rate). AKU-MY01 expresses CD138, CD38, CDI9, CD20, CD45, MUC1, XBP1, Lambda light chain and LMP-l. This was followed by examining IHC expression of LMP1 and CSC markers in 137 MM bone marrow trephine biopsies. LMP1 expression was found in non-neoplastic progenitor mononuclear cells (pMNCs) in 80% and in MM cells in 7% of the cases. LMP1 expression in pMNCs conferred significant survival advantage irrespective of expression of CSC markers (p-value < 0.01).. Prognostic significance of CD34, CD117, ALDH1, CD20, CD45, CD56, XBP1 and MUC I was also examined. Combinatorial group analysis of XBP1 and MUC1 stratified patients into two prognostic groups Good prognosis (XBP1+/ MUC1-), and Worst prognosis (XBP1+/MUC1+) (p-value 0.06). Interaction between XBP1 and MUC1 was associated with adverse outcome. The potential functional relation between MUC1 and XBP-1 was studied next. MUC 1 and XBP-1 was downregulated by RNAi oligos in three different tumour cell lines MCF 7, RPMI and U266. The effect of down regulation of MUC1 and XBP1 on stem cell markers (ABCG2, Oct-4 and Sox2) and cell cycle was also studied. Down regulation of MUC1 resulted in up regulation of XBP1, downregulation of stem cell markers and cell cycle arrest demonstrating the potential role of MUC1 and XBP1 in MM. Further studies need to be undertaken to unravel the exact mechanism of MUC1 regulation on XBP1, effect of over expression on cell cycle, response to in vitro treatment by drugs and the role of EBV in the pathogenesis of MM.
Rajput, S. K. (2020). MUCH1-XBP1 crosstalk in multiple myeloma (Unpublished doctoral thesis). Aga Khan University, Karachi, Pakistan.