Mitochondrial chaperone, TRAP1 modulates mitochondrial dynamics and promotes tumor metastasis

Highlights

• TRAP1 overexpression induces mitochondrial fission, whereas TRAP1 knockdown induces mitochondrial fusion.

• TRAP1 overexpression induces cell proliferation and tumor aggression.

• TRAP1 overexpression induces altered homing properties of tumor cells.

Abstract

Mitochondria play a central role in regulating cellular energy metabolism. However, the present understanding of mitochondria has changed from its unipotent functions to pluripotent and insists on understanding the role of mitochondria not only in regulating the life and death of cells, but in pathological conditions such as cancer. Unlike other cellular organelles, subtle alterations in mitochondrial organization may significantly influence the balance between metabolic networks and cellular behavior. Therefore, the delicate balance between the fusion and fission dynamics of mitochondrion can indicate cell fate. Here, we present mitochondrial chaperone TRAP1 influence on mitochondrial architecture and its correlation with tumor growth and metastasis. We show that TRAP1 overexpression (TRAP1 OE) promotes mitochondrial fission, whereas, TRAP1 knockdown (TRAP1 KD) promotes mitochondrial fusion. Interestingly, TRAP1 OE or KD had a negligible effect on mitochondrial integrity. However, TRAP1 OE cells exhibited enhanced proliferative potential, while TRAP1 KD cells showing increased doubling time. Further, TRAP1 dependent mitochondrial dynamic alterations appeared to be unique since mitochondrial localization of TRAP1 is a mandate for dynamic changes. The expression patterns of fusion and fission genes have failed to correlate with TRAP1 expression, indicating a possibility that the dynamic changes can be independent of these genes. In agreement with enhanced proliferative potential, TRAP1 OE cells also exhibited enhanced migration in vitro and tumor metastasis in vivo. Further, TRAP1 OE cells showed altered homing properties, which may challenge site-specific anticancer treatments. Our findings unravel the TRAP1 role in tumor metastasis, which is in addition to altered energy metabolism.

Introduction

Against the conventional understanding that mitochondria are powerhouses of cells, the emerging studies on mitochondria suggest that they are involved in regulating several cellular functions. Mitochondria are capable of going through fusion or fission in response to various intracellular or extracellular signals, indicating that they exist in a dynamic state between these two forms (Bereiter-Hahn and Voth, 1994, Youle and van der Bliek, 2012, Lee and Yoon, 2016). While maintenance of mitochondrial dynamics are under the regulatory control of membrane-associated GTPases (Thompson, 2002, Tilokani et al., 2018), the disruption of the mitochondrial network can promote apoptosis (Suen et al., 2008, Leboucher et al., 2012, Pyakurel et al., 2015). Mitochondrial dynamics play essential roles in cell cycle regulation (Horbay and Bilyy, 2016), differentiation (Seo et al., 2018), spermatogenesis (Honda and Hirose, 2003), immune metabolism (Angajala et al., 2018), calcium homeostasis (Kowaltowski et al., 2019) and many more. The exposure of cells to nutrient starvation induces mitochondrial fusion (Chang et al., 2019), while exposure to oxidative stress results in mitochondrial fission (Yu et al., 2019). In gross terms, mitochondrial dynamics appear to correlate with the functional state of cells.

The alterations in mitochondrial dynamics also correlate with pathological states (El-Hattab et al., 2018). These include diabetes (Fealy et al., 2018, Dube et al., 2020), cardiovascular diseases (Carreira et al., 2011, Dorn, 2016, Ong and Hausenloy, 2017), and cancer (Cuyas et al., 2018, Anderson et al., 2018, Han et al., 2018). Mitochondria are considered to be obsolete for cancer cells as they sustain oxygen deprivation despite compromised mitochondrial oxidative phosphorylation (OXPHOS) by activating alternate energy metabolism (Warburg et al., 1927, Solaini et al., 2011, Zhang and Yang, 2013). It is in agreement with Warburg’s hypothesis that cancer cells switch to glycolysis in the compromise of OXPHOS (Lebelo et al., 2019, Lu et al., 2015). Interestingly, the Warburg’s theory does not discuss the details of mitochondrial fate during the metabolic switch over. The assumptions include that dysfunctional mitochondria favors cancer progression, thus acts as a trigger for a metabolic switch over (Senyilmaz and Telema, 2015), and enforced OXPHOS inhibition triggers autophagy, a catabolic process (Daskalakis et al., 2020, Maes and Agostinis, 2014). The deregulated balance between fission–fusion dynamics of mitochondria also contributes to dysfunctional mitochondria (Chen and Chan, 2017). Since mitochondrial fusion facilitates ATP production by keeping tricarboxylic acid cycle (TCA) and OXPHOS in loop, mitochondrial fission thought to disconnect TCA and OXPHOS and sensitizes mitochondria to oxidative stress leading to autophagy or apoptosis (Yao et al., 2019).

Among the Hsp90 family of chaperones, Hsp90 predominantly contributes to tumor progression, which is due to its ability to stabilize the functions of mutated proteins, especially the oncogenic kinases (Sreedhar et al., 2004, Citri et al., 2006). While endoplasmic reticulum chaperone, Grp94 contributes to unfolded protein response (ER^UPR) and host immunity (Li et al., 2019), its mitochondrial homolog, TRAP1 functions are not precise. Meanwhile, the TRAP1 role in tumor progression is emerging, and it is implicated in metabolic reprogramming (Masgras et al., 2017, Ramkumar et al., 2020). The TRAP1 involvement in mitochondrial fate determination and cancer progression are reported independently (Takamura et al., 2012, Zhang et al., 2015). Since mitochondria are sensitive to the alterations in cellular redox homeostasis, calcium, and protein homeostasis, these processes may have a considerable influence on mitochondrial dynamics.

Earlier, we showed that TRAP1 overexpression triggers the cellular metabolism despite dysfunctional OXPHOS (Ramkumar et al., 2020). In the present study, we have extended our study to understand how mitochondrial dynamics link TRAP1 to tumor progression. We demonstrate that TRAP1 overexpression induces mitochondrial fission while TRAP1 knockdown favors mitochondrial fusion. We present the involvement of TRAP1 in regulating mitochondrial dynamics and tumor metastasis. Since the interest in understanding the mitochondria role in tumor progression is continuously increasing, our findings gain importance.