A central role for Stat3 in IL-6-induced regulation of growth and differentiation in M1 leukemia cells
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K Nakajima1, Y Yamanaka, K Nakae
1Department of Molecular Oncology, Osaka University Medical School, Japan.
Abstract:
Interleukin-6 (IL-6) induces either differentiation or growth of a variety of cells. Little is known about the molecular basis of this cellular decision. The family of signal transducer and activator of transcription (Stat) proteins are involved in signaling through a variety of cytokine and growth factor receptors, although their biological roles have not been established. To address whether Stat proteins play roles in IL-6-induced growth or differentiation, we introduced two types of mutant Stat3 acting in a dominant-negative manner into M1 leukemic cells which respond to IL-6 with growth arrest and terminal differentiation. We show that dominant-negative forms of Stat3 inhibited both IL-6-induced growth arrest at G(0)/G1 and macrophage differentiation in the M1 transformants. Blocking of Stat activation resulted in inhibition of IL-6-induced repression of c-myb and c-myc. Furthermore, IL-6 enhanced the growth of M1 cells primarily through shortening the length of the G1 period when Stat3 was suppressed. Thus IL-6 generates both growth-enhancing signals and growth arrest- and differentiation-inducing signals at the same time. Stat3 may be a key molecule which determines the cellular decision from cell growth to differentiation in M1 cells.
Insights
Signal transducer and activator of transcription 3 (Stat3) is crucial for Interleukin-6 (IL-6)-induced cell differentiation and growth arrest. Suppressing Stat3 in M1 cells reveals IL-6
Area of Science:
- Cellular biology
- Molecular signaling
- Cancer research
Background:
- Interleukin-6 (IL-6) influences cell fate, promoting either differentiation or growth.
- The precise molecular mechanisms governing IL-6's dual effects remain largely unknown.
- Signal transducer and activator of transcription (Stat) proteins are implicated in cytokine signaling but their specific roles are unclear.
Purpose of the Study:
- To investigate the role of Stat proteins in mediating IL-6-induced cellular responses.
- To determine if Stat3 is a key regulator in the decision between cell growth and differentiation.
Main Methods:
- Introduction of dominant-negative Stat3 mutants into M1 leukemic cells.
- Analysis of IL-6-induced growth arrest at the G(0)/G1 phase.
- Assessment of macrophage differentiation.
- Evaluation of c-myb and c-myc gene expression.
- Investigation of IL-6's effect on G1 phase duration.
Main Results:
- Dominant-negative Stat3 inhibited IL-6-induced growth arrest and differentiation in M1 cells.
- Stat3 activation blockade prevented IL-6-mediated repression of c-myb and c-myc.
- IL-6 accelerated M1 cell growth by shortening the G1 phase when Stat3 was suppressed.
Conclusions:
- IL-6 simultaneously generates signals for growth and for growth arrest/differentiation.
- Stat3 acts as a critical molecular switch, determining the cellular outcome of IL-6 signaling in M1 cells.