A rare fraction of drug-resistant follicular lymphoma cancer stem cells interacts with follicular dendritic cells to maintain tumourigenic potential.

Follicular lymphoma (FL) comprises nearly 25% of non-Hodgkin lymphoma cases and is clinically characterized by initial sensitivity to chemotherapy followed by relapse. FL stroma contains a special type of stromal cell found in the germinal centre of lymph nodes-the follicular dendritic cell (FDC). We first isolated tumourigenic cells from the FL cell line FLK-1 by side population (SP) technique, and found that SP cells, which express ABCG2, were enriched by chemotherapy and radiation treatments. In vitro, SP cells were attracted by and adhered to FDCs through chemokine (C-X-C motif) ligand 12/chemokine (C-X-C motif) receptor 4 (CXCL12/CXCR4) signalling. In vivo, limiting dilution assays showed SP cells were highly enriched in cancer stem cells (CSC), but required FDC for tumour formation in non-obese diabetic/severe combined immunodeficiency mice. Treatment with AMD3100, a specific CXCL12/CXCR4 inhibitor, eliminated tumour growth. These findings were then verified with FL cells isolated from an FL patient's ascitic fluid (FLA-1). Finally, we detected the ABCG2 expressing lymphoma cells in FL clinical specimens. Thus, we found that the highly tumourigenic FL cells having CSC-like activities (FL-SC) interact with FDCs in a CXCL12/CXCR4 dependent manner to resist chemotherapy. Our results indicate the importance of FL-SC and niche cell signalling in maintaining tumourigenicity. These signals represent novel targets for CSC eradication.

Membrane lipid biosynthesis in Chlamydomonas reinhardtii: expression and characterization of CTP:phosphoethanolamine cytidylyltransferase.

CTP:phosphoethanolamine cytidylyltransferase (ECT) is considered to be the regulatory enzyme in the CDP-ethanolamine pathway of phosphatidylethanolamine (PE) biosynthesis. The ECT cDNA of Chlamydomonas reinhardtii encodes a protein of 443 amino acid residues, which is longer than the same protein in yeast, rat or human. The translated product of cloned cDNA was expressed as a fusion protein in Escherichia coli, and was shown to have ECT activity. The deduced amino acid sequence has 41% identity with that of human or rat, and 30% with yeast. The ECT protein has a repetitive internal sequence in its N- and C-terminal halves and a signature peptide sequence, RTXGVSTT, typical of the cytidylyltransferase family. The first 70 amino acid residues do not match the N-terminal part of the cytidylyltransferases from other organisms, and we hypothesize that it is a subcellular targeting signal to mitochondria. ECT and organelle marker enzyme assays showed that the total activity of ECT correlates well with that of fumarase, a marker enzyme for mitochondria. Northern blots showed an increase in mRNA abundance during reflagellation, indicating a possibility of transcriptional regulation. A notable change in the enzyme activity in C. reinhardtii cells was observed during the cell cycle, increasing during the dark and then decreasing during the light period, while the mRNA level did not alter, providing evidence for post-translational regulation.