DEL

SQLE Deficiency and Cholesterol Auxotrophy in ALK⁺ ALCLs

This study explores the cholesterol dependency of cancer cells, particularly in ALK⁺ anaplastic large cell lymphoma (ALCL) cell lines (ALK⁺ ALCLs). Garcia-Bermudez et al. discovered that these cells rely heavily on cholesterol uptake due to a loss of squalene monooxygenase (SQLE), identifying the low-density lipoprotein receptor (LDLR) as crucial for their growth, presenting a potential therapeutic target. Using gene expression data from the cancer cell line encyclopedia (CCLE), Garcia-Bermudez et al. identified nine cell lines lacking SQLE mRNA and protein. Remarkably, six of these belong to the ALK⁺ ALCLs: DEL, SU-DHL-1, KIJK, SUP-M2, SR-786, and Karpas 299 (Fig. 1d and e). Similar to SNU-1, these SQLE-deficient ALCL cell lines are sensitive to cholesterol depletion and accumulate high levels of squalene (Fig. 1g and f). SRS microscopy revealed that ALK+ALCLs accumulate squalene in lipid droplets (Fig. 1h). The loss of SQLE expression is linked to promoter hypermethylation, with DNA-hypomethylating agents upregulating SQLE mRNA. Primary tumor samples and patient-derived xenografts of ALK⁺ ALCLs also showed reduced SQLE expression. Despite the inverse correlation between NPM-ALK translocation and SQLE expression, ALK signaling modulation did not affect SQLE expression, suggesting a different silencing mechanism (Fig. 2). These findings indicate that ALK⁺ ALCLs lack SQLE expression, making them cholesterol auxotrophs.

Fig. 1. ALK⁺ ALCLs are auxotrophic for cholesterol due to lack of SQLE expression (Garcia-Bermudez, J., Baudrier, L., et al., 2019).

Fig. 2. Lack of SQLE expression in primary ALK⁺ ALCLs (Garcia-Bermudez, J., Baudrier, L., et al., 2019).

ALK Inhibitor Crizotinib Reduces ACLY Y682 Phosphorylation in ALK⁺ Lymphoma and Neuroblastoma Cells

Rapid cell proliferation requires metabolic adaptation for biomass synthesis, with ATP citrate lyase (ACLY) playing a crucial role in linking carbohydrate and lipid metabolism. Basappa J et al. investigated the role of tyrosine phosphorylation at Y682 in enhancing ACLY activity and its oncogenic implications in multiple cancers. Phosphoproteomics analysis of lymphoma cell lines with NPM-ALK fusion tyrosine kinase identified 881 phosphorylated tyrosine peptides. Key findings indicate that ACLY Y682 phosphorylation significantly correlates with ALK Y1604 activation. ALK inhibition via CEP-26939 reduced ACLY Y682 phosphorylation, confirmed by Crizotinib (an ALK inhibitor) treatment (Fig. 3f). They treated two ALK+ ALCL cell lines (SUDHL-1, DEL) and one neuroblastoma cell line (NB1) with Crizotinib, observing reduced Y682 phosphorylation through anti-pACLY Y682 antibody immunoblotting (Fig. 3a). Immunohistochemistry on biopsies from ALK+ and ALK- ALCL patients showed a strong correlation between ACLY Y682 phosphorylation and ALK expression (Fig. 3b). Creating an ALK+ ALCL cell line (DEL) with either an empty vector, HA-tagged ACLY-WT, or ACLY-Y682F, immunoblotting revealed increased Y682 phosphorylation in ACLY-WT but not in ACLY-Y682F cells (Fig. 3c). Additionally, transducing primary human T cells with either active NPM-ALK or kinase-deficient NPM-ALK-K210R showed ACLY Y682 phosphorylation only in cells with active NPM-ALK (Fig. 3e).

Fig. 3. NPM-ALK interacts with ACLY and phosphorylates on Y682 residue in ALK⁺ALCLs (Basappa J., ElAzzouny, M. A., et al., 2020).