Genetic abnormalities in Waldenström's macroglobulinemia

Aberrant posttranscriptional processing of hyaluronan synthase 1 in malignant transformation and tumor progression

It is becoming increasingly apparent that splicing defects play a key role in cancer, and that alterations in genomic splicing elements promote aberrant splicing. Alternative splicing increases the diversity of the human transcriptome and increases the numbers of functional gene products. However, dysregulation that leads to aberrant pre-mRNA splicing can contribute to cancer. Hyaluronan (HA), known to be an important component of cancer progression, is synthesized by hyaluronan synthases (HASs). In cancer cells, hyaluronan synthase 1 (HAS1) pre-mRNA is abnormally spliced to generate a family of aberrant splice variants (HAS1Vs) that synthesize extracellular and intracellular HA. HAS1Vs are clinically relevant, being found almost exclusively in malignant cells. Expression of aberrant HAS1Vs predicts poor survival in multiple myeloma. In this review, we summarize the unusual properties of HAS1Vs and their relationship to cancer. HAS1Vs form heterogeneous multimers with normally spliced HAS1 as well as with each other and with HAS3. Aberrant variants of HAS1 synthesize HA. Extracellular HA synthesized by HAS1Vs is likely to promote malignant spread. We speculate that synthesis of intracellular HA plays a fundamental and early role in oncogenesis by promoting genetic instability and the emergence of viable cancer variants that lead to aggressive disease.

Alteration of introns in a hyaluronan synthase 1 (HAS1) minigene convert Pre-mRNA [corrected] splicing to the aberrant pattern in multiple myeloma (MM): MM patients harbor similar changes

Aberrant pre-mRNA splice variants of hyaluronan synthase 1 (HAS1) have been identified in malignant cells from cancer patients. Bioinformatic analysis suggests that intronic sequence changes can underlie aberrant splicing. Deletions and mutations were introduced into HAS1 minigene constructs to identify regions that can influence aberrant intronic splicing, comparing the splicing pattern in transfectants with that in multiple myeloma (MM) patients. Introduced genetic variations in introns 3 and 4 of HAS1 as shown here can promote aberrant splicing of the type detected in malignant cells from MM patients. HAS1Vd is a novel intronic splice variant first identified here. HAS1Vb, an intronic splice variant previously identified in patients, skips exon 4 and utilizes the same intron 4 alternative 3′splice site as HAS1Vd. For transfected constructs with unaltered introns 3 and 4, HAS1Vd transcripts are readily detectable, frequently to the exclusion of HAS1Vb. In contrast, in MM patients, HAS1Vb is more frequent than HAS1Vd. In the HAS1 minigene, combining deletion in intron 4 with mutations in intron 3 leads to a shift from HAS1Vd expression to HAS1Vb expression. The upregulation of aberrant splicing, exemplified here by the expression of HAS1Vb, is shown here to be influenced by multiple genetic changes in intronic sequences. For HAS1Vb, this includes enhanced exon 4 skipping and increased usage of alternative 3′ splice sites. Thus, the combination of introduced mutations in HAS1 intron3 with introduced deletions in HAS1 intron 4 promoted a shift to an aberrant splicing pattern previously shown to be clinically significant. Most MM patients harbor genetic variations in intron 4, and as shown here, nearly half harbor recurrent mutations in HAS1 intron 3. Our work suggests that aberrant intronic HAS1 splicing in MM patients may rely on intronic HAS1 deletions and mutations that are frequent in MM patients but absent from healthy donors.