Suppression of isoprenylcysteine carboxylmethyltransferase compromises DNA damage repair

DNA damage is a double-edged sword for cancer cells. On the one hand, DNA damage–induced genomic instability contributes to cancer development; on the other hand, accumulating damage compromises proliferation and survival of cancer cells. Understanding the key regulators of DNA damage repair machinery would benefit the development of cancer therapies that induce DNA damage and apoptosis. In this study, we found that isoprenylcysteine carboxylmethyltransferase (ICMT), a posttranslational modification enzyme, plays an important role in DNA damage repair. We found that ICMT suppression consistently reduces the activity of MAPK signaling, which compromises the expression of key proteins in the DNA damage repair machinery. The ensuing accumulation of DNA damage leads to cell cycle arrest and apoptosis in multiple breast cancer cells. Interestingly, these observations are more pronounced in cells grown under anchorage-independent conditions or grown in vivo. Consistent with the negative impact on DNA repair, ICMT inhibition transforms the cancer cells into a “BRCA-like” state, hence sensitizing cancer cells to the treatment of PARP inhibitor and other DNA damage–inducing agents.

MicroRNA-99a-5p suppresses cell proliferation, migration, and invasion by targeting isoprenylcysteine carboxylmethyltransferase in oral squamous cell carcinoma

Background MicroRNA (miR)-99a-5p acts as a tumor suppressor in several tumors, including bladder cancer and breast cancer, but its biological function in oral squamous cell carcinoma (OSCC) is poorly understood. Methods miR-99a-5p expression was determined in OSCC tissues and cell lines using quantitative reverse transcription polymerase chain reaction (RT-qPCR). Cell proliferation was assessed by the Cell Counting Kit-8 assay and colony formation assay. Wound healing and Transwell assays were used to analyze migration and invasion abilities, respectively, in OSCC cells. The luciferase reporter assay, RT-qPCR, and western blotting were used to determine the relationship between miR-99a-5p and isoprenylcysteine carboxylmethyltransferase (ICMT). Results miR-99a-5p expression in OSCC tissues and cell lines was significantly decreased compared with corresponding controls, and was significantly associated with clinical stage and lymph node metastasis in OSCC. Functional assays revealed that miR-99a-5p overexpression significantly inhibited the proliferation, migration, and invasion abilities of CAL-27 and TCA-8113 OSCC cells. miR-99a-5p was found to directly target ICMT, while ICMT restoration reversed the role of miR-99a-5p in OSCC cells. Conclusions Our results indicate that miR-99a-5p-mediates the down-regulation of ICMT, which could be used as a novel potential therapeutic target for OSCC treatment.

A small-molecule ICMT inhibitor delays senescence of Hutchinson-Gilford progeria syndrome cells

A farnesylated and methylated form of prelamin A called progerin causes Hutchinson-Gilford progeria syndrome (HGPS). Inhibiting progerin methylation by inactivating the isoprenylcysteine carboxylmethyltransferase (ICMT) gene stimulates proliferation of HGPS cells and improves survival of Zmpste24-deficient mice. However, we don't know whether Icmt inactivation improves phenotypes in an authentic HGPS mouse model. Moreover, it is unknown whether pharmacologic targeting of ICMT would be tolerated by cells and produce similar cellular effects as genetic inactivation. Here, we show that knockout of Icmt improves survival of HGPS mice and restores vascular smooth muscle cell numbers in the aorta. We also synthesized a potent ICMT inhibitor called C75 and found that it delays senescence and stimulates proliferation of late-passage HGPS cells and Zmpste24-deficient mouse fibroblasts. Importantly, C75 did not influence proliferation of wild-type human cells or Zmpste24-deficient mouse cells lacking Icmt, indicating drug specificity. These results raise hopes that ICMT inhibitors could be useful for treating children with HGPS.

Isoprenylcysteine carboxylmethyltransferase-based therapy for Hutchinson–Gilford progeria syndrome

ABSTRACTProgerin is a mutant prelamin A variant that causes Hutchinson–Gilford progeria syndrome (HGPS, progeria), a rare genetic disease characterized by premature aging and death in childhood. Although several therapeutic approaches have been explored in experimental models, clinical trials have shown very limited benefits in HGPS patients. Here, we describe the development of UCM-13207, a new potent inhibitor of isoprenylcysteine carboxylmethyltransferase (ICMT) that reduces progerin nuclear accumulation and ameliorates the typical alterations in progeroid human and mouse cells. UCM-13207 also improves phenotypic anomalies and extends lifespan in progerin-expressing LmnaG609G/G609G mice. These results support the potential use of UCM-13207 as a new treatment for progeria.

An in vivo inflammatory loop potentiates KRAS blockade

ABSTRACTKRAS inhibitors perform inferior to other targeted drugs. To investigate a possible reason for this, we treated cancer cells with KRAS inhibitors deltarasin (targeting phosphodiesterase-δ), cysmethynil (targeting isoprenylcysteine carboxylmethyltransferase), and AA12 (targeting KRASG12C), and silenced/overexpressed mutant KRAS using custom vectors. We show that KRAS-mutant tumor cells exclusively respond to KRAS blockade in vivo, because the oncogene co-opts host myeloid cells via a C-C-motif chemokine ligand 2/interleukin-1β signaling loop for sustained tumorigenicity. Indeed, KRAS-mutant tumors did not respond to deltarasin in Ccr2 and Il1b gene-deficient mice, but were deltarasin-sensitive in wild-type and Ccr2-deficient mice adoptively transplanted with wild-type murine bone marrow. A KRAS-dependent pro-inflammatory transcriptome was prominent in human cancers with high KRAS mutation prevalence and predicted poor survival. Hence the findings support that in vitro systems are suboptimal for anti-KRAS drug screens, and suggest that interleukin-1β blockade might be specific for KRAS-mutant cancers.