No abstract

Interleukin-5 (IL-5) induction of c-Myc expression is associated with IL-5 inhibition of apoptosis in hematopoietic cells. In this study, TFalpha1 and TFalpha8 cells with stable overexpression of IL-5 receptor alpha (IL-5Ralpha) subunit in TF-1 cells, a human hematopoietic progenitor cell line which expressed low levels of IL-5Ralpha, were used to explored how IL-5 up-regulate c-Myc and the role of c-Myc in IL-5 signaling. First, we demonstrate that IL-5 induced c-Myc RNA and protein expressions, as well as activated Janus kinases (JAK1 and JAK2) and signal transducer and activator of transcription-5b (STAT5b). JAK inhibitor AG490 and c-Myc inhibitor 10058-F4, both, reduced IL-5-mediated cell proliferation in a dose- and time-dependent manner. Both, AG490 and 10058-F4, also reduced IL-5-mediated anti-apoptotic activity. Furthermore, AG490 inhibited IL-5-mediated c-Myc induction and promoter activity. We further examined the role of JAK1 and JAK2 in the induction of c-Myc expression using the CDJAK fusion proteins, which consisted of a CD16 extracellular domain, a CD7 transmembrane domain, and either JAK1 (CDJAK1) or JAK2 (CDJAK2) as intracellular domains. Simultaneous activation of JAK1 and JAK2 by anti-CD16 antibody crosslinking of CDJAK1 and CDJAK2 could induced c-Myc expression and promoter activity; AG490 inhibited CDJAK1 and CDJAK2-mediated effects. These results suggest that IL-5 induces cell proliferation and anti-apoptosis through the JAK/c-Myc pathway, and that JAK1 and JAK2 activation participate in IL-5-induced up-regulation of c-Myc.

Chronic myeloid leukemia (CML) is caused by a constitutively active BCR-ABL tyrosine kinase. Tyrosine kinase inhibitors (TKIs) imatinib and its derivatives represent a breakthrough for CML therapy, but the use of TKI alone is ineffective for many CML patients. CD69, an early activation marker of lymphocytes, participates in immune and inflammatory responses. Previous studies revealed that BCR-ABL upregulates CD69 expression; however, the role of CD69 in CML cells is unknown. Here, we demonstrate that BCR-ABL induced CD69 promoter activity and mRNA and protein expression via the NF-κB pathway. CD69 knockdown partially increased apoptosis and expression of erythroid differentiation markers, α-globin, ζ-globin, and glycophorin A, and increased imatinib sensitivity in K562 and KU812 CML cells. Gene microarray analysis and quantitative real-time PCR verified that CD24, an oncogenic gene, downregulated in K562 cells upon CD69 knockdown. CD69 overexpression increased, whereas CD69 knockdown inhibited CD24 promoter activity and mRNA and protein levels. CD24 knockdown also partially increased apoptosis, erythroid differentiation, and imatinib sensitivity in K562 cells, whereas its overexpression inhibited the effects of CD69 knockdown on apoptosis, erythroid differentiation, and imatinib sensitivity in K562 cells. Imatinib-induced apoptosis and erythroid differentiation were also inhibited by CD69 or CD24 overexpression in BCR-ABL-expressing CML cell lines and CD34 cells. Taken together, CD24 is a downstream effector of CD69. CD69 and CD24 partially inhibit apoptosis and erythroid differentiation in CML cells; thus, they may be potential targets to increase imatinib sensitivity.