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AMY-1, a novel C-MYC binding protein that stimulates transcription activity of C-MYC
1Faculty of Pharmaceutical Sciences, Hokkaido University, Kita 12 Nishi 6, Kita-ku, Sapporo 060 Japan.
Background:
The c-myc proto-oncogene has been suggested to play key roles in cell proliferation, differentiation, transformation and apoptosis. A variety of functions of C-MYC, the product of c-myc, are attributed to protein-protein interactions with various cellular factors including Max, YY1, p107, Bin1 and TBP. Max and YY1 bind to the C-terminal region of C-MYC, while p107, Bin1 and TBP bind to the N-terminal region covering myc boxes. The N-terminal region is involved in all the biological functions of C-MYC, and different proteins are therefore thought to interact with the N-terminal region of C-MYC to display different functions.
Results:
We cloned two cDNAs which encode a novel C-MYC-binding protein of 11 kDa, designated AMY-1 (Associate of C-MYC). The two cDNAs, AMY-1L and AMY-1S, derived from alternative usage of polyadenylation signals, code for the same protein of 11 kDa. AMY-1 was bound via its C-terminal region to the N-terminal region of C-MYC (amino acids nos 58-148) corresponding to the transactivation domain. AMY-1 was localized in the cytoplasm in cells expressing c-myc at low levels, but in the nucleus in the cells of a high c-myc expression in transiently transfected cells. A similar difference in endogenous AMY-1 localization was observed during the cell cycle: AMY-1 translocated from cytoplasm to nucleus during the S phase when c-myc expression was increased. AMY-1 by itself did not recognize the E-box element, the MYC/Max binding sequence, nor did it transactivate via the element, but stimulated the activation of E-box-regulated transcription by MYC/Max. FISH analyses revealed that the amy-1 gene was located at 1p32.2-1p33 in human genome.
Conclusions:
AMY-1 is a 11 kDa protein which binds to the N-terminal region of C-MYC and stimulates the activation of E-box-dependent transcription by C-MYC. AMY-1, which mostly localizes in the cytoplasm, translocates into the nucleus in the S phase of the cell cycle upon an increase of c-myc expression, and may thus control the transcriptional activity of C-MYC.
Insights
A novel 11 kDa protein, AMY-1, binds to C-MYC and enhances its transcriptional activity. AMY-1 translocates to the nucleus during the S phase, potentially regulating C-MYC
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- The c-myc proto-oncogene is crucial for cell proliferation, differentiation, transformation, and apoptosis.
- C-MYC interacts with various cellular factors, including Max, YY1, p107, Bin1, and TBP, through its N-terminal and C-terminal regions.
- The N-terminal region of C-MYC is essential for its biological functions, with different interacting proteins mediating distinct roles.
Purpose of the Study:
- To identify and characterize novel proteins that interact with C-MYC.
- To investigate the functional role of a newly discovered C-MYC-binding protein, AMY-1, in transcriptional regulation.
Main Methods:
- Cloning of cDNAs encoding the novel C-MYC-binding protein, AMY-1.
- Analysis of AMY-1 protein interactions with C-MYC using biochemical assays.
- Cellular localization studies (cytoplasmic vs. nuclear) under varying c-myc expression levels and during the cell cycle.
- Functional assays to assess AMY-1's effect on E-box-regulated transcription.
- Fluorescence in situ hybridization (FISH) to determine the chromosomal location of the amy-1 gene.
Main Results:
- Two cDNAs, AMY-1L and AMY-1S, were cloned, both encoding an 11 kDa protein, AMY-1.
- AMY-1 binds to the N-terminal transactivation domain of C-MYC (amino acids 58-148).
- AMY-1 localizes to the cytoplasm at low c-myc levels and translocates to the nucleus when c-myc expression is high or during S phase.
- AMY-1 does not bind or transactivate the E-box element itself but enhances MYC/Max-mediated transcription.
- The amy-1 gene is mapped to chromosome 1p32.2-1p33.
Conclusions:
- AMY-1 is an 11 kDa protein that binds to C-MYC's N-terminal region and potentiates E-box-dependent transcription.
- AMY-1's dynamic localization between cytoplasm and nucleus, particularly during S phase with increased c-myc expression, suggests a role in controlling C-MYC transcriptional activity.