AMY‐1, a novel C‐MYC binding protein that stimulates transcription activity of C‐MYC

Open Access
Publisher Website
Google Scholar
Abstract
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.