Par-complex aPKC and Par3 cross-talk with innate immunity NF-κB pathway in epithelial cells

Area of Science:

• Cell Biology
• Molecular Biology
• Immunology

Background:

• The Par-complex, including atypical protein kinase C (aPKC) and Par3, is known to be downregulated during NF-κB activation in intestinal epithelial cells.
• The precise role of aPKC and Par3 in pro-inflammatory responses, particularly concerning NF-κB signaling, remains unclear in this context.

Purpose of the Study:

• To investigate the role of aPKC and Par3 in regulating NF-κB activation and pro-inflammatory responses in intestinal epithelial cells.
• To determine if aPKC and Par3 act as inhibitors or activators of the canonical NF-κB pathway.

Main Methods:

• Caco-2 human colon carcinoma cells were transduced with lentiviral particles expressing constitutively active (ca) PKCι or anti-Par3 shRNA.
• NF-κB activity was assessed using a luminescence reporter assay.
• The effect of Par3 knockdown on TNFα-induced inflammatory gene transcription (IL-8, GRO-1, GRO-2, GRO-3) was analyzed.

Main Results:

• Constitutively active PKCι decreased baseline NF-κB activity in Caco-2 cells, unlike its effect in non-polarized HEK293 cells.
• A PKCι mutant lacking the PB1 domain, which does not localize to the tight-junction, also decreased NF-κB activity.
• Knockdown of Par3 increased baseline NF-κB activity and significantly enhanced the response to TNFα, leading to increased transcription of inflammatory genes.

Conclusions:

• Atypical PKC and Par3 function as inhibitors of the canonical NF-κB activation pathway in intestinal epithelial cells.
• These proteins may play a role in regulating pro-inflammatory responses, potentially through independent pathways.
• Findings suggest a novel inhibitory role for the Par-complex in NF-κB signaling within the intestinal epithelium.