With an estimated 604,000 new cases and 342,000 deaths in 2020, cervical cancer (CC) is the fourth most prevalent gynecological malignancy worldwide [1]. Sadly more than 80% of CC-related mortality is reported in developing and underdeveloped countries [2]. The age range for the onset of carcinoma in situ and invasive cancer is 30–35 years and 45–55 years, respectively [3]. Pap testing and screening for human papillomavirus (HPV) infection have helped to reduce the global CC burden [4]. On the other hand, CC is still the primary contributor to gynecological cancer in several nations, and its prevalence among younger people is rising [5]. Persistent infection with high-risk HPV, genetic and epigenetic changes in the host, and the HPV genome may play a crucial role in CC progression [6]. Despite advances in diagnosis and treatment, the complete molecular mechanism facilitating CC pathogenesis remains obscure. Thus, delineating the molecular mechanisms and cellular changes may uncover disease intricacies and ameliorate the clinical management of CC.

Mitochondria are double membranous complex intracellular organelles crucial for producing cellular energy [7]. Besides, mitochondria participate in the modulation of innate immunity, calcium (Ca2+) homeostasis, metabolism, oxidative radicals production, biomolecule synthesis, signal transduction, and apoptosis [8]. We and others have shown a close association between mitochondrial dysfunction and CC [9]. Mitochondrial functional alterations can help to gain cancer hallmarks and therapy resistance in CC [[10], [11], [12]]. Studies from our laboratory have shown a reduction in mtDNA content and a substantial increase in mtDNA mutation in CC patients compared with control subjects [9]. D-loop of mitochondria showed the maximum number of nucleotide variations [9]. Many anticancer agents hamper CC progression by inducing mitochondrial dysfunction. For instance, compounds such as aesculetin [13], vosaroxin [14], pachymic acid [15], chrysin, and capsaicin [16] have affected mitochondrial functions by stimulating reactive oxygen species (ROS) production, membrane potential depolarization, AMPK signaling, ATP depletion and apoptosis in CC condition. Thus, targeting mitochondrial structure and function could be used as a CC management strategy.

Lipids are essential for normal homeostasis of the cells and critical for maintaining membrane integrity, as well as a source of energy and signaling molecule that regulates cell proliferation, metabolism, and apoptosis [17]. Disturbances to lipid homeostasis are closely associated with several diseases, including cancer. Mitochondrial lipids are vital for preserving mitochondrial membrane integrity [18]. Mitochondria are the primary site for ROS production [19]. ROS can attack lipids in the mitochondrial membrane, specifically polyunsaturated fatty acids, accelerating lipid peroxidation (LPO) [20]. The reactive lipids generated by LPO can disrupt the integrity and functioning of mitochondria, leading to its dysfunction and may promote carcinogenesis or cell death [21]. A rise in intracellular Ca2+ has been shown to induce ROS and membrane LPO [20]. The Ca2+-ROS-dependent LPO is positively correlated with apoptosis induction and negatively linked to cell migration, growth, and proliferation [22]. Thus, Ca2+, oxidative stress, and LPO may be interconnected, and activation of the Ca2+-oxidative stress-LPO axis may impede tumor progression.

Double C2 like Domain Beta (DOC2B), residing at 17p13.3, belongs to the C2-like domain protein family and encodes for a 45.94kDa protein. DOC2B is a ubiquitously expressed Ca2+-dependent protein that participates in various cellular functions, including vesicular trafficking, exocytosis, membrane remodeling, insulin and glucose homeostasis, and release of neurotransmitters [[23], [24], [25]]. Diseases such as diabetes, leukemia, oral cancer, invasive breast cancer, and CC show reduced expression of DOC2B [23,[26], [27], [28], [29]]. Previously, we reported DOC2B as a metastatic suppressor in CC [30]. Both premalignant and malignant CC samples showed DOC2B downregulation via promoter hypermethylation. Overexpression and knockdown studies demonstrated DOC2B to suppress the growth, proliferation, migration, and invasion of CC cells. Additionally, we have demonstrated that DOC2B induces senescence and inhibits epithelial-to-mesenchymal transition (EMT) and Wnt signaling [30,31]. DOC2B may serve as an early diagnostic marker and a new therapeutic target in CC.

Herein, we hypothesized that the tumor growth regulatory functions of DOC2B might be due to the induction of mitochondrial structural and functional alterations. To explore this, we have overexpressed and knockdown DOC2B in SiHa and Cal27 cells, respectively, and showed for the first time that DOC2B translocates to mitochondria and promotes lipotoxicity. DOC2B manipulation (i) induced morphological changes in mitochondria, (ii) decreased mitochondrial DNA (mtDNA) copy number, mitochondrial mass (MM), and mitochondrial membrane potential (MMP) with a concomitant increase in intracellular ATP, intracellular O.-2, mitochondrial and intracellular Ca2+, and (iii) reduced glucose uptake and lactate production. DOC2B impaired mitochondrial biogenesis, evidenced by its fragmented morphology and downregulation of key proteins associated with maintaining mitochondrial structure. Finally, we showed that enhanced LPO in the presence of DOC2B is a Ca2+ and O.-2-dependent process. Our findings reveal that DOC2B promotes lipid accumulation and LPO via oxidative stress through intracellular Ca2+ overload, which may contribute to mitochondrial dysfunction. Collectively, we recommend targeting the DOC2B–Ca2+-oxidative stress-LPO-mitochondrial axis could be helpful in improved CC management. Further induction of lipotoxicity in tumor cells by activating DOC2B may serve as a novel therapeutic approach in CC.