Duplication and diversification of the spermidine/spermine N1-acetyltransferase 1 genes in zebrafish

Spermidine/spermine N(1)-acetyltransferase 1 (Ssat1) is a key enzyme in the polyamine interconversion pathway, which maintains polyamine homeostasis. In addition, mammalian Ssat1 is also involved in many physiological and pathological events such as hypoxia, cell migration, and carcinogenesis. Using cross-genomic bioinformatic analysis in 10 deuterostomes, we found that ssat1 only exists in vertebrates. Comparing with mammalian, zebrafish, an evolutionarily distant vertebrate, contains 3 homologous ssat1 genes, named ssat1a, ssat1b, and ssat1c. All zebrafish homologues could be transcribed and produce active enzymes. Despite the long history since their evolutionary diversification, some features of human SSAT1 are conserved and subfunctionalized in the zebrafish family of Ssat1 proteins. The polyamine-dependent protein synthesis was only found in Ssat1b and Ssat1c, not in Ssat1a. Further study indicated that both 5' and 3' sequences of ssat1b mediate such kind of translational regulation inside the open reading frame (ORF). The polyamine-dependent protein stabilization was only observed in Ssat1b. The last 70 residues of Ssat1b were crucial for its rapid degradation and polyamine-induced stabilization. It is worth noting that only Ssat1b and Ssat1c, but not the polyamine-insensitive Ssat1a, were able to interact with integrin α9 and Hif-1α. Thus, Ssat1b and Ssat1c might not only be a polyamine metabolic enzyme but also simultaneously respond to polyamine levels and engage in cross-talk with other signaling pathways. Our data revealed some correlations between the sequences and functions of the zebrafish family of Ssat1 proteins, which may provide valuable information for studies of their translational regulatory mechanism, protein stability, and physiological functions.

Procedure volume of gastric cancer resections versus 5-year survival

AIM

We used nationwide, population-based data to examine associations between hospital and surgeon volumes of gastric cancer resections and their patients' short-term and long-term survival likelihood.

METHODS

The study uses 1997-1999 inpatient claims data from Taiwan's National Health Insurance linked to "cause of death" data for 1997-2004. The total cohort of 6909 gastric cancer resection patients were categorized by their surgeon's/hospital's procedure volume, and examined for differences in 6-month mortality and 5-year mortality (post 6 months), by procedure volume, using Cox proportional hazard regressions, adjusting for surgeon, hospital and patient characteristics. We hypothesized that surgeons' case volume and age but not hospital volume will predict short-term and long-term survival.

RESULTS

Adjusted estimates show that increasing surgeon volume predicts better 6-month survival (adjusted mortality hazard ratio = 1.3 for low-volume surgeons relative to very high-volume surgeons; p < 0.01) and 5-year survival (adjusted mortality hazard ratios = 1.3; p < 0.001 for low-volume; 1.2 with p < 0.01 for medium volume) and increasing surgeon's age (adjusted hazards ratio = 1.4 for age < 41 years relative to 41-50 years; p < or = 0.001; 0.8 for > or = 51 years relative to 41-50 years; p < 0.05). In hospital volume regressions, surgeon's age is a consistent and significant predictor, not hospital volume. Findings suggest a key role of experience in surgical skill and sensitivity for early stage diagnosis in gastric cancer survival.

CONCLUSIONS

Although a key study limitation is the lack of cancer stage data, the pattern of findings suggests that experienced surgeons have relatively better survival outcomes among gastric cancer patients.