ABSTRACT
Cellular compartments are coordinated through a dynamic bidirectional communication network amongst various
organelles. Here, we focus on the communication between mitochondria and the nucleus, organelles that each
possess their own genomes. The mitochondrial and nuclear genomes have co-evolved for over a billion years and
have likely required close communication and cross-regulation. However, whereas mitochondria are known to be
regulated by over 1,000 nuclear-encoded proteins, but there is currently no known mitochondrial-encoded factor
that actively communicates to and regulates the nucleus. We have recently identified a novel gene encoded within
the mitochondrial DNA and named it MOTS-c (Mitochondrial ORF within the Twelve S rRNA type-c). MOTS-c is a
small 16 amino acid peptide that regulates metabolic homeostasis, in part, via the master nutrient sensor AMPK
(adenosine monophosphate-activated protein kinase). We recently reported that MOTS-c can translocate into the
nucleus in response to metabolic stress to bind to chromatin and regulate nuclear gene expression. Further, our
preliminary study using a multi-pronged approach, including single cell RNA-seq, bioinformatics (including machine
learning), chromatin immunoprecipitation (ChIP) coupled with quantitative PCR (qPCR), and cell sorting, showed
that MOTS-c can regulate cellular proliferation; MOTS-c targeted the p53/p21 pathway and ribosomal processes.
Considering the important metabolic role of mitochondria in cellular proliferation processes (29), a critical question
that remains largely enigmatic is how mitochondrial-encoded factors communicate to the nucleus to coordinate the
metabolic shift with gene expression during proliferation. Notably, rapidly dividing cancer cells had undetectable levels
of MOTS-c or nuclear-translocation deficiency, suggesting loss of mito-nuclear communication by MOTS-c.
Together, cancer may be a genetic disease in which our two genomes exist in a state of disrupted bi-directional
communication/regulation, and may serve as a unique model to start understanding the role of MOTS-c in cellular
proliferation. Because MOTS-c expression/function was dysregulated and that MOTS-c can negatively regulate
cell cycle/proliferation, we hypothesize that MOTS-c is a mitochondrial-encoded tumor suppressor, the first of its kind
to be identified, that directly regulates the nucleus to coordinate cellular metabolism with proliferation. We propose three
aims to test this hypothesis. First, we will characterize MOTS-c as a tumor suppressor that regulates cell proliferation at
the molecular, cellular, genetic level. Second, we will comprehensively map the MOTS-c-dependent functional nuclear
genomic landscape using multiple complimentary genomics approach, including single cell RNA-seq, ATAC-seq
(chromatin accessibility), and genomic footprinting using ChIP-seq. The data from each genomic approach will be
integrated using cutting-edge computational methods, including machine learning, to decipher the message(s) MOTS-
c delivers to the nuclear genome to regulate cancer cell proliferation and survival. Lastly, we will determine how MOTS-
c-mediated communication to the nucleus can differentially regulate cellular proliferation and stress resistance in normal
and malignant cells using mouse models of cancer.
If successful, we predict that our study will have broad and lasting impact on (i) basic research by introducing the
paradigm-shifting concept of mitochondrial-encoded tumor suppressors that coordinate cellular metabolism and
proliferation and (ii) therapeutic development by revealing mtDNA as a source of novel drug targets (currently there
are no FDA-approved drugs based on the mitochondrial genome).