SELECTIVE SUPPRESSION OF COMPLEMENT EXPRESSION BY AHR

Open Access
Author:
Shpilsky, Jason Evan
Area of Honors:
Biochemistry and Molecular Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Chen Pei David Tu, Thesis Supervisor
  • Gary H Perdew, Thesis Supervisor
  • Chen Pei David Tu, Honors Advisor
  • Wendy Hanna Rose, Faculty Reader
Keywords:
  • Aryl hydrocarbon receptor
  • Complement System
  • AHR
Abstract:
The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor noted for its role in the metabolism of dioxin and other environmental xenobiotics. However, recent research has shown an expanded role of AHR in pro- and anti-inflammatory signaling through DNA-dependent and independent modes of action. AHR-mediated suppression of acute-phase response genes, such as cytokines and complement proteins, has previously been shown in heptatoma cells. The complement system is an effective, non-specific mechanism of identifying and destroying damaged or foreign cells. Often, tumor cells express complement inhibitory proteins, such as CD55 and Factor H (CFH), to avoid detection by the complement system and promote proliferation. Expanding upon previously published work on AHR-mediated suppression of complement genes, a therapeutic pathway using AHR was explored in MCF-7 breast cancer cells and several head and neck squamous carcinoma cell (HNSCC) lines. As canonical DNA-dependent AHR activation of phase I metabolism genes has noted deleterious effects, a selective AHR modulator (SAHRM) was used to induce an AHR effect instead of an agonist. The flavonoid 3’, 4’-dimethoxy-α-naphthoflavone (DiMNF) has been used successfully in previous research as a SAHRM to repress cytokine-mediated complement induction. The ability to selectively repress expression of complement inhibitory proteins by tumor cells invokes a potential mode of natural cancer clearance by the organism. MCF-7 cells were determined to be an inconclusive model for complement as they do not express factor H. DiMNF (10 μM) treatment of HNSCC lines exhibited inconsistent effects on each cell line. Although CFH and CD55 expression levels of mRNA and protein were expected to decrease, only one cell line (HNSCC-13) exhibited this effect. Two other lines, HNSCC-15 and -30, showed an inverse pattern of increase and decrease between the two complement proteins, possibly suggesting a compensatory mechanism. HNSCC-2095 and HNSCC–9 did not present any observable DiMNF-mediated effects. Although it appears that DiMNF does mediate a significant level of attenuation of CD55 and CFH protein levels in certain cases, further study into the relationship between AHR and the complement system is required before a viable therapeutic application is can be explored.