Subject(s)
Gene Expression Profiling , Leukemia, Lymphocytic, Chronic, B-Cell , Survival Analysis , Adult , Aged , Aged, 80 and over , Female , Humans , Leukemia, Lymphocytic, Chronic, B-Cell/genetics , Leukemia, Lymphocytic, Chronic, B-Cell/mortality , Leukemia, Lymphocytic, Chronic, B-Cell/therapy , Male , Middle Aged , Real-Time Polymerase Chain ReactionABSTRACT
The t(10;11)(p13;q14) translocation results in the fusion of the CALM (clathrin assembly lymphoid myeloid leukemia protein) and AF10 genes. This translocation is observed in acute myeloblastic leukemia (AML M6), acute lymphoblastic leukemia (ALL) and malignant lymphoma. Using a yeast two-hybrid screen, the four and a half LIM domain protein 2 (FHL2) was identified as a CALM interacting protein. Recently, high expression of FHL2 in breast, gastric, colon, lung as well as in prostate cancer was shown to be associated with an adverse prognosis. The interaction between CALM and FHL2 was confirmed by glutathione S-transferase-pulldown assay and co-immunoprecipitation experiments. The FHL2 interaction domain of CALM was mapped to amino acids 294-335 of CALM. The transcriptional activation capacity of FHL2 was reduced by CALM, but not by CALM/AF10, which suggests that regulation of FHL2 by CALM might be disturbed in CALM/AF10-positive leukemia. Extremely high expression of FHL2 was seen in acute erythroid leukemia (AML M6). FHL2 was also highly expressed in chronic myeloid leukemia and in AML with complex aberrant karyotype. These results suggest that FHL2 may play an important role in leukemogenesis, especially in the case of AML M6.
ABSTRACT
The transcription factor CCAAT enhancer-binding protein alpha (C/EBPalpha) has an important role in granulopoiesis. The tumor suppressor function of C/EBPalpha is shown by the findings that loss of expression or function of C/EBPalpha in leukemic blasts contributes to a block in myeloid cell differentiation and to leukemia. C/EBPalpha mutations are found in around 9% of acute myeloid leukemia (AML) patients. The mechanism by which the mutant form of C/EBPalpha (C/EBPalpha-p30) exerts a differentiation block is not well understood. By using a proteomic screen, we have recently reported PIN1 as a target of C/EBPalpha-p30 in AML. In the present study, we show that C/EBPalpha-p30 induces PIN1 expression. We observed elevated PIN1 expression in leukemic patient samples. Induction of C/EBPalpha-p30 results in recruitment of E2F1 in the PIN1 promoter. We show that the inhibition of PIN1 leads to myeloid differentiation in primary AML blasts with C/EBPalpha mutations. Overexpression of PIN1 in myeloid cells leads to block of granulocyte differentiation. We also show that PIN1 increases the stability of the c-Jun protein by inhibiting c-Jun ubiquitination, and c-Jun blocks granulocyte differentiation mediated by C/EBPalpha. Our data suggest that the inhibition of PIN1 could be a potential strategy of treating AML patients with C/EBPalpha mutation.
