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MSSP promotes ras/myc cooperative cell transforming activity by binding to c-Myc
1Graduate School of Pharmaceutical Sciences and; College of Medical Technology, Hokkaido University, Kita-ku, Sapporo 060-0812, Japan.
Background:
MSSPs, myc single strand binding proteins, were originally identified as proteins recognizing a putative replication origin/transcriptional enhancer in the human c-Myc gene. The cDNAs encoding four of the family proteins, MSSP-1, MSSP-2, Scr2 and Scr3, were cloned. These proteins carry two copies of the putative RNA binding domains, RNP-A and RNP-B, and have been suggested to participate in DNA replication and cell cycle progression from the G1 to the S phase.
Results:
We report that MSSP-1 and MSSP-2 bound directly to the C-terminal portion of c-Myc, along with Max, side by side. MSSP, c-Myc and Max formed a ternary complex in vivo, although MSSP did not directly associate with Max. The MSSP/Myc/Max ternary complex lost the binding activity to the E-box sequence-the recognition sequence of c-Myc/Max complex-thereby abrogating the E-box-dependent transcription activity of c-Myc. MSSP specifically stimulated the cooperative transforming activity of c-myc with ras, in a manner dependent upon the RNP sequences, while mssp itself showed no transforming activity in mouse NIH3T3 cells. The NIH3T3 transformants, together with ras, myc and mssp, grew to form very large colonies in soft agar, as compared to those with ras plus myc or ras alone.
Conclusions:
MSSP is a modulator of c-Myc and the c-Myc/MSSP complex may deregulate cell cycle controls and lead cells towards transforming pathways.
Insights
Myc single-strand binding proteins (MSSPs) bind c-Myc and Max, forming a ternary complex. This complex inhibits c-Myc
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Myc single-strand binding proteins (MSSPs) are implicated in DNA replication and cell cycle control.
- MSSPs bind to RNA and DNA, with four family members identified: MSSP-1, MSSP-2, Scr2, and Scr3.
- These proteins possess two RNA recognition motifs (RNP-A and RNP-B).
Purpose of the Study:
- To investigate the interaction between MSSPs and the c-Myc oncoprotein.
- To determine the functional consequences of MSSP binding to c-Myc.
Main Methods:
- Co-immunoprecipitation assays to detect complex formation in vivo.
- Analysis of DNA binding activity of the MSSP/c-Myc/Max complex.
- Transformation assays in NIH3T3 cells to assess oncogenic potential.
Main Results:
- MSSP-1 and MSSP-2 directly bind to the C-terminus of c-Myc, forming a ternary complex with Max.
- The MSSP/c-Myc/Max complex loses affinity for the E-box DNA sequence, inhibiting c-Myc transcriptional activity.
- MSSP enhances the transforming activity of c-Myc in NIH3T3 cells, promoting anchorage-independent growth.
Conclusions:
- MSSP acts as a modulator of c-Myc function.
- The c-Myc/MSSP complex can disrupt cell cycle regulation and promote cellular transformation.