Alteration of the lipid profile in lymphomas induced by MYC overexpression

Abstract

Overexpression of the v-myc avian myelocytomatosis viral oncogene homolog (MYC) oncogene is one of the most commonly implicated causes of human tumorigenesis. MYC is known to regulate many aspects of cellular biology including glucose and glutamine metabolism. Little is known about the relationship between MYC and the appearance and disappearance of specific lipid species. We use desorption electrospray ionization mass spectrometry imaging (DESI-MSI), statistical analysis, and conditional transgenic animal models and cell samples to investigate changes in lipid profiles in MYC-induced lymphoma. We have detected a lipid signature distinct from that observed in normal tissue and in rat sarcoma-induced lymphoma cells. We found 104 distinct molecular ions that have an altered abundance in MYC lymphoma compared with normal control tissue by statistical analysis with a false discovery rate of less than 5%. Of these, 86 molecular ions were specifically identified as complex phospholipids. To evaluate whether the lipid signature could also be observed in human tissue, we examined 15 human lymphoma samples with varying expression levels of MYC oncoprotein. Distinct lipid profiles in lymphomas with high and low MYC expression were observed, including many of the lipid species identified as significant for MYC-induced animal lymphoma tissue. Our results suggest a relationship between the appearance of specific lipid species and the overexpression of MYC in lymphomas.

Keywords: biostatistics; cancer; lipidomics; metabolomics; transgenic models.

Fig. 1.

DESI-MSI of MYC-induced lymphomas shows specific lipid signature. Representative negative ion mode DESI mass spectra of (A) MYC-induced lymphoma (sample lymphoma A) and (B) normal control thymus (samples T02) tissues in the m/z 700–1,100 range are shown. Results for Western blot analysis of MYC and α-tubulin are shown in C for MYC-induced lymphomas samples A, B, and C, and normal thymus controls samples TY, T01, T02. DESI-MS ion images of selected molecular ions at m/z 885.5478, m/z 773.5321, m/z 788.5435, and m/z 795.5163 are shown in D for lymphoma and control samples.

Fig. 2.

Different lipid profiles are observed in MYC-induced versus RAS-induced lymphoma cell lines. Representative negative ion mode DESI mass spectra of (A) MYC-induced lymphoma cells: (Top) MYC ON; (Middle) MYC OFF 4 h; (Bottom) MYC OFF 16 h and (B) RAS-induced lymphoma cells: (Top) RAS ON; (Middle) RAS OFF 4 h; (Bottom) RAS OFF 16 h.

Fig. 3.

Lipid profiles of human lymphomas with high MYC expression are similar to that observed in MYC-induced mouse lymphomas. Pie charts display the average normalized abundance of selected lipid species for three samples of MYC-induced lymphoma, nine samples of human lymphomas (HL01, HL02, HL04, HL10, HL12, HL14, HL15, HL17, and HL18) with high MYC expression (>0.2 RLU) and six samples of human lymphomas (HL05, HL06, HL07, HL08, HL09, and HL13) with low MYC expression (<0.2 RLU). The lipids selected were found to be increased [PG(18:1/16:1), PG(18:2/18:1), PG(18:1/18:1), PG(20:4/18:1), and PG(18:1/22:6)] or decreased [PS(16:0/18:1), PE(18:0/20:4), PS(18:0/18:1), PS(18:0/20:3), and PI(18:0/20:4)] in MYC-induced lymphoma by SAM with FDR = 0% and statistical scores |d| > 2. The “others” category refer to the sum of the average normalized abundances of the less abundant lipids: PE(P-16:0/20:4), CL(20:3/18:1/18:1/16:1), PE(18:0/18:2), PE(P-16:0/22:6), PG(18:2/20:4), PS(P-18:0/20:4), PS(18:0/22:6), and PI(18:0/18:2).