BCR and B-cell chronic lymphocytic leukemia: However, the downregulation of MCL1 could also be explained by the decreased expression of Wnt pathway molecules (LEF1 and ROR1), TCL1, BCR signaling molecules (PI3K and BTK) and c-MYC that were shown to positively regulate MCL1 expression to promote CLL B-cells survival [11, 14, 28].