How cancer cells make and respond to interferon-I.

Area of Science:

• Immunology
• Cancer Biology
• Molecular Biology

Background:

• Type I interferons (IFN-I) exhibit context-dependent effects in cancer, inducing apoptosis at high concentrations and promoting survival at low concentrations.
• The transcription factor IFN-stimulated gene (ISG) factor 3 (ISGF3) mediates IFN-I responses, with its tyrosine-phosphorylated form driving acute effects and the unphosphorylated form (U-ISGF3) mediating prosurvival mechanisms.

Purpose of the Study:

• To elucidate the complex and often opposing roles of IFN-I in cancer progression.
• To investigate the novel cell-intrinsic functions of programmed cell death-ligand 1 (PD-L1) in modulating IFN-I responses within tumor cells.

Main Methods:

• Analysis of cellular responses to varying concentrations of IFN-I.
• Investigation of ISGF3 phosphorylation states and their functional consequences.
• Assessment of PD-L1 expression and its impact on IFN-I signaling and tumor cell survival.

Main Results:

• Tyrosine-phosphorylated ISGF3 mediates acute, detrimental IFN-I effects like growth arrest and apoptosis.
• Unphosphorylated ISGF3 (U-ISGF3) drives essential prosurvival mechanisms under chronic low-level IFN-I exposure.
• PD-L1 exhibits protumorigenic activity by suppressing acute IFN-I responses and sustaining beneficial low-level IFN-I signaling.

Conclusions:

• IFN-I signaling in cancer is complex, with distinct outcomes dependent on concentration and ISGF3 phosphorylation status.
• PD-L1 plays a critical cell-intrinsic role in promoting tumor survival by modulating IFN-I responses.
• A deeper understanding of these intricate IFN-I and PD-L1 interactions may reveal novel therapeutic strategies for cancer treatment.