A putative interaction between mitochondrial cytochrome c oxidase subunit II (COX II) to lamin A/C and LAP2α in colon epithelial cells.

Abstract

The lamina is a cage-like structure, composed of lamins, found underneath the inner nuclear membrane (INM). In mammals, Lamins are type V intermediate filaments. Three genes encode seven different lamin proteins. These genes are
LMNA, LMNB1 and LMNB2. Lamins are classified into A- and B-types. A-type lamins, Lamin A, Lamin C, Lamin Aδ10 and Lamin C2, are mainly expressed in differentiated tissues. All encodes by the LMNA gene and products of alternative
splicing. Recent studies have shown the expression of Lamin A/C in colon crypt epithelia cells. This expression was greater in differentiated epithelial and stem cells than in the proliferation zone. Since 1999, mutations in LMNA have been shown to cause several different inherited diseases in muscle, fat, bone, skin and nerve tissues. LAP2α is one of the strong binding partners to Lamin A/C. LAP2α has a specific function as a non-membrane protein associated with the nucleoskeleton and may help to organize higher order chromatin structure by interacting with Lamin A/C.
To understand more about Lamin A/C and LAP2α in colon epithelial development,a Yeast 2-hybrid screen was used to look for novel protein interactions to Lamin A/C and/or LAP2a. It was found Cytochrome c oxidase subunit II (Cox2) is a putative binding partner to Lamin A/C and LAP2 α. Cox2 is encoded by the mitochondrial genome and imported into complex IV (COX) of the mitochondrial respiratory chain (MRC). The majority of mitochondrial proteins are encoded by
nuclear DNA. However, 13 essential subunits of the MRC are encoded by mtDNA. The MRC is composed of five multi-subunit complexes (I-V). MRC is implicated in ATP generation and is involved in apoptosis in response to different stimuli.
Deficiency in COX in colon cancer cells results in resistance to apoptosis and increases in reactive oxygen species (ROS). Biochemical assays like Coimmunopreciptation
(IP) and western blot (WB) and Immuno-gold labeling (TEM)
were used. IP confirmed the putative interaction of Cox2 to Lamin A/C and LAP2α. WB showed the expression of lamin A/C and LAP2α in the mitochondrial and nuclear fractions but not in cytosol. TEM is alternative method showed the
distribution of lamin A/C and LAP2α in the nucleus and mitochondria.