May be involved in p53/TP53 mediated inhibition of cellular proliferation in response to DNA damage. Binds to and inhibits cyclin-dependent kinase activity, preventing phosphorylation of critical cyclin-dependent kinase substrates and blocking cell cycle progression. Functions in the nuclear localization and assembly of cyclin D-CDK4 complex and promotes its kinase activity towards RB1.

At higher stoichiometric ratios, inhibits the kinase activity of the cyclin D-CDK4 complex (PubMed:25329316). Inhibits DNA synthesis by DNA polymerase delta by competing with POLD3 for PCNA binding (By similarity). Plays an important role in controlling cell cycle progression and DNA damage-induced G2 arrest (By similarity)

Interacts with HDAC1; the interaction is prevented by competitive binding of C10orf90/FATS to HDAC1 facilitating acetylation and protein stabilization of CDKN1A/p21 (PubMed:20154723). Interacts with MKRN1. Interacts with PSMA3.

Interacts with PCNA. Component of the ternary complex, cyclin D-CDK4-CDKN1A. Interacts (via its N-terminal domain) with CDK4; the interaction promotes the assembly of the cyclin D-CDK4 complex, its nuclear translocation and promotes the cyclin D-dependent enzyme activity of CDK4.

Binding to CDK2 leads to CDK2/cyclin E inactivation at the G1-S phase DNA damage checkpoint, thereby arresting cells at the G1-S transition during DNA repair. Interacts with PIM1 (By similarity). Interacts with STK11 (PubMed:25329316).

Interacts with NUAK1 (By similarity). Interacts with DTL and TRIM39 (By similarity). Interacts with PKP3; the interaction sequesters CDKN1A to the cytoplasm thereby repressing its role as an inhibitor of CDK4- and CDK6-driven RB1 phosphorylation (PubMed:36689330)

Expressed in keratinocytes (at protein level)

The C-terminal is required for nuclear localization of the cyclin D-CDK4 complex

The PIP-box K+4 motif mediates both the interaction with PCNA and the recruitment of the DCX(DTL) complex: while the PIP-box interacts with PCNA, the presence of the K+4 submotif, recruits the DCX(DTL) complex, leading to its ubiquitination