# USP35 Acts as a Deubiquitinating Enzyme for ID3 to Promote Immune Escape in Colorectal Cancer

## TL;DR

This study reveals how USP35 helps colorectal cancer cells avoid the immune system by stabilizing ID3, and how inhibiting USP35 with IU1 can reverse this immune evasion.

## Contribution

The discovery that USP35 acts as a deubiquitinating enzyme for ID3, and that its inhibition with IU1 enhances immunotherapy efficacy in CRC.

## Key findings

- USP35 stabilizes ID3 by deubiquitinating lysine residues K2 and K30, increasing PD-L1 expression and immune escape.
- IU1 inhibits USP35 activity, promotes ID3 degradation, and reduces PD-L1 expression.
- IU1 enhances anti-tumor immune responses and improves the efficacy of PD-L1 monoclonal antibody therapy.

## Abstract

Our prior investigation has demonstrated that ID3 modulates PD‐L1, thereby affecting immune evasion in colorectal cancer (CRC). Nonetheless, the regulatory mechanisms of ID3, particularly those involving its ubiquitination and degradation, remain inadequately understood. In this study, we identify USP35 as a deubiquitinating enzyme for ID3, which stabilizes ID3 by targeting the N‐terminal lysine residues K2 and K30, thus inhibiting its ubiquitination and degradation. This stabilization enhances ID3's transcriptional activity, resulting in elevated PD‐L1 expression in CRC and facilitating immune escape. Furthermore, we discover an effective inhibitor of USP35 enzyme activity, IU1, which directly suppresses ID3 expression by promoting its ubiquitination and subsequently reducing PD‐L1 expression. IU1 not only impedes tumor cell proliferation, but also augments the efficacy of PD‐L1 monoclonal antibody therapy by enhancing anti‐tumor immune responses. These findings elucidate a novel mechanism by which the USP35‐ID3‐PD‐L1 axis contributes to immune evasion in CRC and propose a potential therapeutic strategy to improve the efficacy of immunotherapy in CRC patients.

USP35 stabilizes ID3 expression by deubiquitinating the K2/K30 site, thereby upregulating PD‐L1 and promoting immune escape in colorectal cancer. IU1, an inhibitor of USP35 enzyme activity, has been shown to inhibit USP35, thereby accelerating ID3 degradation, enhancing CD8+ T cell killing, and reversing the immunosuppressive microenvironment.