Cancer-associated protein kinase C mutations reveal kinase's role as tumor suppressor

Area of Science:

• Oncology
• Molecular Biology
• Biochemistry

Background:

• Protein kinase C (PKC) isozymes are implicated in cancer, but their precise role remains debated.
• Phorbol esters, potent PKC ligands, are known tumor promoters, complicating the understanding of PKC's function in cancer.
• Mutations in PKC isozymes are found in human cancers, but their functional impact is not fully characterized.

Purpose of the Study:

• To investigate the functional impact of Protein kinase C (PKC) mutations in human cancers.
• To determine whether PKC isozymes act as oncogenes or tumor suppressors.
• To explore therapeutic strategies targeting PKC in cancer.

Main Methods:

• Analysis of 8% of PKC mutations identified in human cancers.
• Functional assessment of loss-of-function mutations, including impact on second-messenger binding, phosphorylation, and catalysis.
• CRISPR-mediated genome editing to correct a PKCβ mutation in a colon cancer cell line.
• Xenograft tumor growth models.
• Bioinformatic analysis of mutation co-occurrence with cancer drivers.

Main Results:

• The majority of analyzed PKC mutations were loss-of-function; none were activating.
• Loss-of-function mutations affected all PKC subgroups and impaired key enzymatic functions.
• Correction of a PKCβ mutation suppressed cancer cell growth in vitro and in vivo.
• PKCβ was found to be haploinsufficient for tumor suppression.
• Some mutations exhibited dominant-negative effects, suppressing global PKC signaling.
• PKC mutations were suggested to cooperate with other cancer-driving mutations.

Conclusions:

• Protein kinase C (PKC) isozymes generally function as tumor suppressors.
• Cancer therapies should aim to restore, rather than inhibit, PKC activity.
• Understanding PKC mutation types is crucial for developing effective cancer treatments targeting these pathways.