Background: Colon cancer affects one in five Australians by the age of 75, and results in ~4,700 deaths each year. Most colon cancers (>80%) arise from inherited mutations in the mutation cluster region of the adenomatous polyposis coli (APC) gene, and are linked to initiation of colon tumour progression due to disruption of APC protein function. We previously discovered that mutated APC proteins accumulate strongly at mitochondria and promote survival of APC-mutant tumour cells. This study now examines a novel and unanticipated role for APC in mitochondrial transport.
Methods: APC and potential regulatory partner proteins, (for example Miro/Milton protein complex involved in mitochondrial transport), were overexpressed in cells by transient or stable transfection, or silenced by siRNA, and any changes in protein and mitochondrial distribution observed by immuno-fluorescence microscopy. Changes in protein expression were also noted through western blotting techniques. Immunoprecipitation (IP) assays were performed to investigate binding of APC full length and mutant forms to potential partners involved in mitochondrial transport.
Results: APC silencing by RNAi interference in U2OS, HDF1314 (wild type APC) and SW480 (APC truncated) cell lines caused extensive perinuclear clustering of mitochondria similar to that observed when certain APC fragments were overexpressed. Preliminary experiments showed that the Miro/Milton complex colocalised with APC at membrane protrusions and IP results suggest a potential interaction between these proteins.
Conclusions: This preliminary data suggests that APC may modulate mitochondrial transport, which in turn may play a role in colon cancer pathogenesis by targeted delivery of ATP reserves to motile membrane regions at the cell periphery. Improved understanding of the role of APC is essential for more effective design of chemotherapeutic treatments.