ABSTRACT: The nucleolus is a subnuclear compartment with a key role in ribosome biogenesis and cellular stress responses. These mechanisms are governed by a complex interaction of proteins, including the NOC1 network. This study reveals a novel relationship between NOC1 and MYC transcription factor, known for its key role in controlling ribosomal biogenesis and cell growth and proliferation. Here, we demonstrate that NOC1 functions as a direct target of MYC, as it is transcriptionally induced through a functional MYC-binding E-box sequence in the NOC1 promoter region. Furthermore, interactome analysis reveals that NOC1-complex includes the nucleolar proteins NOC2 and NOC3 and other nucleolar components such as Nucleostemin1 Ns1 and mainly components for the transport of ribosomal subunits and maturation and with components for rRNA processing. In response to MYC, NOC1 expression and localization within the nucleolus significantly increase, suggesting a direct functional link between MYC activity and NOC1 function. Notably, NOC1 over-expression leads to the formation of large nuclear granules and enlarged nucleoli, which co-localize with nucleolar fibrillarin and Ns1. Additionally, we demonstrate that NOC1 expression is necessary for Ns1 nucleolar localization, suggesting a role for NOC1 in maintaining nucleolar structure. Finally, the co-expression of NOC1 and MYC enhances the formation of abnormal structures formed by NOC1 within the nucleolus, outlining another aspect of NOC1 and MYC cooperation in nucleolar dynamics. This study reveals NOC1's interactions with proteins involved in RNA processing, modification, and splicing, such as Ythdc1, Flacc, and spenito. These proteins play key roles in mediating N6-methyladenosine (m6A) methylation of mRNAs. NOC1's potential involvement in coordinating RNA splicing and nuclear mRNA export highlights its significance in regulating gene expression. In summary, our study uncovers novel roles for NOC1 in nucleolar homeostasis and establishes its direct connection with MYC in the network governing nucleolar structure and function. These findings also highlight NOC1's interaction with proteins relevant for RNA processing, modification, and splicing, suggesting a broader role in addition to its control of nucleolar homeostasis, providing new insight into NOC1 function that can be further investigated into its function in regulating cellular growth and proliferation.
Romina Belli 
