posted on 2020-03-10, 15:31authored byHeon Shin, Hyun-Jeong Cha, Min Jung Lee, Keun Na, Donha Park, Chae-Yeon Kim, Dai Hoon Han, Hoguen Kim, Young-Ki Paik
Various liver diseases,
including hepatocellular carcinoma (HCC),
have been linked to mitochondrial dysfunction, reduction of reactive
oxygen species (ROS), and elevation of nitric oxide (NO). In this
study, we subjected the human liver mitochondrial proteome to extensive
quantitative proteomic profiling analysis and molecular characterization
to identify potential signatures indicative of cancer cell growth
and progression. Sequential proteomic analysis identified 2452 mitochondrial
proteins, of which 1464 and 2010 were classified as nontumor and tumor
(HCC) mitochondrial proteins, respectively, with 1022 overlaps. Further
metabolic mapping of the HCC mitochondrial proteins narrowed our biological
characterization to four proteins, namely, ALDH4A1, LRPPRC, ATP5C1,
and ALDH6A1. The latter protein, a mitochondrial methylmalonate semialdehyde
dehydrogenase (ALDH6A1), was most strongly suppressed in HCC tumor
regions (∼10-fold decrease) in contrast to LRPPRC (∼6-fold
increase) and was predicted to be present in plasma. Accordingly,
we selected ALDH6A1 for functional analysis and engineered Hep3B cells
to overexpress this protein, called ALDH6A1-O/E cells. Since ALDH6A1
is predicted to be involved in mitochondrial respiration, we assessed
changes in the levels of NO and ROS in the overexpressed cell lines.
Surprisingly, in ALDH6A1-O/E cells, NO was decreased nearly 50% but
ROS was increased at a similar level, while the former was restored
by treatment with S-nitroso-N-acetyl-penicillamine.
The lactate levels were also decreased relative to control cells.
Propidium iodide and
Rhodamine-123 staining suggested that the decrease in NO and increase
in ROS in ALDH6A1-O/E cells could be caused by depolarization of the
mitochondrial membrane potential (ΔΨ). Taken together,
our results suggest that hepatic neoplastic transformation appears
to suppress the expression of ALDH6A1, which is accompanied by a respective
increase and decrease in NO and ROS in cancer cells. Given the close
link between ALDH6A1 suppression and abnormal cancer cell growth,
this protein may serve as a potential molecular signature or biomarker
of hepatocarcinogenesis and treatment responses.