A γ‐glutamyl hydrolase lacking the signal peptide confers susceptibility to folates/antifolates in acute lymphoblastic leukemia cells

Abstract

A key cofactor of several enzymes implicated in DNA synthesis, repair, and methylation, folate has been shown to be required for normal cell growth and replication and is the basis for cancer chemotherapy using antifolates. γ‐Glutamyl hydrolase (GGH) catalyzes the removal of γ‐polyglutamate tails of folylpoly‐/antifolylpoly‐γ‐glutamates to facilitate their export out of the cell, thereby maintaining metabolic homeostasis of folates or pharmacological efficacy of antifolates. However, the factors that control or modulate GGH function are not well understood. In this study, we show that intact GGH is not indispensable for the chemosensitivity and growth of acute lymphoblastic leukemia (ALL) cells, whereas GGH lacking N‐terminal signal peptide (GGH−ΔN) confers the significant drug resistance of ALL cells to the antifolates MTX and RTX. In addition, ALL cells harboring GGH−ΔN show high susceptibility to the change in folates, and glycosylation is not responsible for these phenotypes elicited by GGH−ΔN. Mechanistically, the loss of signal peptide enhances intracellular retention of GGH and its lysosomal disposition. Our findings clearly define the in vivo role of GGH in ALL cells and indicate a novel modulation of the GGH function, suggesting new avenues for ALL treatment in future.

Up-regulation of ABCG1 is associated with methotrexate resistance in acute lymphoblastic leukemia cells

“…The LC-MS was performed as previously described ( Wang et al, 2022 ). The standards of MTX-Glu2, MTX-Glu3, MTX-Glu4, and MTX-Glu5 were purchased from Schircks Laboratories (Bauma, Switzerland).…”

“…Alterations in any step of the MTX metabolic pathway can result in cellular resistance. Over the past few years, various mechanisms contributing to MTX resistance have been reported, such as a) impaired uptake due to inactivating mutations or downregulation in RFC1 ( Rothem et al, 2003 ; Rothem et al, 2004 ; Kaufman et al, 2006 ); b) loss of FPGS function due to relapse-specific mutations ( Li et al, 2020 ; Yu et al, 2020 ); c) enhanced GGH activity or expression ( Cole et al, 2001 ; Schneider and Ryan, 2006 ; Kim et al, 2013 ; Wang et al, 2022 ); d) overexpression of DHRF ( Assaraf, 2007 ; Fotoohi and Albertioni, 2008 ); e) augmented drug efflux due to increased expression of the transporters such as ABCB1, ABCC1-4 and ABCG2 ( Volk et al, 2002 ; Ansari et al, 2009 ; Liu et al, 2018 ; Jaramillo et al, 2019 ; Engle and Kumar, 2022 ). It is worth mentioning that the mechanisms underlying clinical resistance to MTX involve multiple factors and are not fully understood.…”