Carboxyl-terminal modulator protein (CTMP) is a tumor suppressor-like binding 
partner of Protein kinase B (PKB/Akt) that negative regulates this kinase. In 
the course of our recent work, we identified that CTMP is consistently 
associated with leucine zipper/EF-hand-containing transmembrane-1 (LETM1). Here, 
we report that adenovirus-LETM1 increased the sensitivity of HeLa cells to 
apoptosis, induced by either staurosporine or actinomycin D. As shown 
previously, LETM1 localized to the inner mitochondrial membrane. 
Electron-microscopy analysis of adenovirus-LETM1 transduced cells revealed that 
mitochondrial cristae were swollen in these cells, a phenotype similar to that 
observed in optic atrophy type-1 (OPA1)-ablated cells. OPA1 cleavage was 
increased in LETM1-overexpressing cells, and this phenotype was reversed by 
overexpression of OPA1 variant-7, a cleavage resistant form of OPA1. Taken 
together, these data suggest that LETM1 is a novel binding partner for CTMP that 
may play an important role in mitochondrial fragmentation via OPA1-cleavage.