The role of TIS11 family in the pathophysiology of chronic lymphocytic leukaemia
In this study the basal expression of Tis 11 family and their regulation in B-CLL cells in response to stimuli that induce apoptosis (crosslinked Rituximab, XRituximab) or stimuli that inhibit spontatieous apoptosis' (IL-4, CD40, CD40+IL-4, PMA) was tested. Tis 11 family bind to AU Rich Elements (AREs) in the 3' Untranslated Region (3'UTR) and induce degradation of mRNAs bearing these target sequences. The Tis 11 family consists of Tis 11, 'Tis 11 b and Tis 11 d which induce apoptosis when overexpressed in a variety of human cell lines (epithelial, osteosarcoma and fibroblasts). It was found that Tis 11 mRNA is strongly expressed in unstimulated B-CLL cells, when compared to Tis 11 b mRNA levels, and was downregulated following stimulation with IL-4 or anti-CD40 at 3 hours post stimulation but remained unaffected by all other stimuli. Tis1l b mRNA was found to be minimally expressed in unstimulated B-CLL cells and was strongly induced following XRituximab, PMA and anti-CD40 treatment in all patients tested but remained unchanged by IL-4 or anti-CD40+IL-4. Finally Tislid was found to be strongly expressed in unstimulated B-CLL cells and was weakly induced by XRituximab and PMA in some but not all patients tested and showed no change after IL-4, anti-CD40 or anti-CD40+IL-4 stimulation. Additionally it was found that when Tis 11 b is induced by XRituximab it is primarily regulated through p38 and to lesser extend through JNK pathway since inhibition of these pathways abrogated induction of the Tis 11 b mRNA and protein. On the contrary when Tis 11b was induced by PMA or anti-CD40 it was found to be regulated through NF-KB pathway since inhibition of this pathway resulted in complete abrogation of Tis11 b mRNA induction following PMA or anti-CD40 stimulation. In order to determine the function that Tis 11 b is involved in reponse to XRituximab and PMA or anti-CD40 treatment, Tisllb siRNA technology was utilised which revealed that inhibition of Tis 11 b significantly reduced (by 50-70%) the efficiency of XRituximab in inducing apoptosis in CLL cells while when Tis 11 b siRNA was applied in PMA or anti-CD40 stimulated CLL cells it significantly reduced their ability to induce plasma cell differentiation in these cells. Thus Tis 11 b is involved in induction of apoptosis following Rituximab treatment in CLL cells and also it is involved in induction of differentiation of CLL cells when such a stimulus (eg: anti-CD40) is present. Finally it was found that Tis 11 bIBerg36 is probably involved in B cell differentiation in general, since it was found that it has different basal expression and regulation at different stages of B cell differentiation represented by Nalm6 (pre-B cells), Ramos (Germinal Centre B cells), AGLeL and WILeL (memory B cells) and RPMI8226 and MM1.S (plasma cells) cell lines. Indeed it was found that Multiple Myeloma cell lines have undetectable levels of Tis 11 bIBerg36 mRNA and neither PMA nor anti-eD40 could induce Tis 11 b in plasma cells even though these stimuli could modify expression of this gene in all other stages of differentiation. Thus Tis 11 family especially Tis 11 b and Tis 11 may have an important role in the pathogenesis or progression of eLL (and possibly of B cell malignancies in general) and necessitate further investigation.