SKA1 induces de novo MTX‐resistance in osteosarcoma through inhibiting FPGS transcription

Abstract

De novo methotrexate (MTX)‐resistance, whose underlying mechanism remains largely unknown, usually leads to very poor prognosis in patients with osteosarcoma (OS). In this study, we established the de novo MTX‐resistant OS cell line SF‐86 and identified the candidate gene spindle and kinetochore associated complex subunit 1 (SKA1) as potentially related to de novo MTX‐resistance. Analysis of a cohort of 95 OS patients demonstrated that SKA1 overexpression significantly correlated with de novo MTX‐resistance and poor 5‐year survival. Mechanistically, SKA1 overexpression lead to a downregulation of folylpoly‐γ‐glutamate synthetase (FPGS), a key enzyme that converts MTX into its active form, MTX‐PG. We further demonstrated that SKA1 interacts with DNA‐directed RNA polymerase II subunit RPB3. ChIP analysis revealed that RPB3 binds the promoter region of the FPGS gene and triggers FPGS transcription upon MTX treatment in SW1353, a MTX‐sensitive OS cell line lacking endogenous SKA1 expression. On the contrary, this process is blocked in SF‐86 cells due to the formation of an inhibitory SKA1‐RPB3 complex. Furthermore, downregulation of SKA1 levels restores MTX sensitivity in SF‐86. Collectively, our study has established the de novo MTX‐resistant cell line SF‐86 and identified SKA1 as a novel regulator of FPGS, playing a key role in the development of de novo MTX‐resistance in OS.

SKA1 promotes tumor metastasis via SAFB-mediated transcription repression of DUSP6 in clear cell renal cell carcinoma

“…Through its carboxy-terminal winged-helix domain, SKA1 engages in interactions with tubulin monomers, which explains how it is structurally supported in its ability to attach microtubule structures [ 17 ]. Additionally, SKA1 inhibits FPGS transcription by physically interacting with RPB3 to cause osteosarcoma cells to become resistant to MTX [ 18 ]. Thus, we reason that SKA1 might form a complex with interacting proteins that are instrumental in its functions in the ccRCC malignant process.…”

“…SKA1 needs to act synergistically with Ndc80 to exert a pro-metastatic activity in the head and neck adenoid cystic carcinoma [ 30 ]. Moreover, SKA1 prevents RNA polymerase II subunit RPB3 from activating FPGS transcription by interacting with RPB3, consequently inducing MTX-resistance in osteosarcoma patients [ 18 ]. Of relevance here, our findings also indicate that SKA1 is mainly localized in the nucleus and interacts with scaffold attachment factor B (SAFB).…”

SKA1 regulates actin cytoskeleton remodelling via activating Cdc42 and influences the migration of pancreatic ductal adenocarcinoma cells

“…Not only SKA1 genomic mutations result in chromosome congression failure and subsequent cell changes, 33 but also SKA1 overexpression itself is primarily responsible for oncogenic function. Besides, SKA1 knock‐down represses proliferation and metastasis in a range of malignancies by regulating the ERK1/2, Akt signalling and cell cycles 16‐17,34,35. These evidences indicate a multifaceted oncogenic effect driven by SKA1.…”

Targeting Molecular Mechanisms Underlying Treatment Efficacy and Resistance in Osteosarcoma: A Review of Current and Future Strategies

“…SKA1 overexpression led to a downregulation of folylpoly-γ-glutamate synthetase (FPGS), a key enzyme in the polyglutamylation of methotrexate, via Ska1 interaction with the RNA polymerase II subunit RPB3. In cell lines, overexpression of SKA1 also led to methotrexate resistance, while SKA1 downregulation was able to restore drug sensitivity [340]. These findings present a new target to which new agents can be directed in order to overcome methotrexate resistance due to alterations in its intracellular metabolism.…”