Mutant strains of Pichia pastoris with enhanced secretion of recombinant proteins.

Although Pichia pastoris is a popular protein expression system, it exhibits limitations in its ability to secrete heterologous proteins. Therefore, a REMI (restriction enzyme mediated insertion) strategy was utilized to select mutant beta-g alactosidase s upersecretion (bgs) strains that secreted increased levels of a ß-galactosidase reporter. Many of the twelve BGS genes may have functions in intracellular signaling or vesicle transport. Several of these strains also appeared to contain a more permeable cell wall. Preliminary characterization of four bgs mutants showed that they differed in the ability to enhance the export of other reporter proteins. bgs13, which has a disruption in a gene homologous to Saccharomyces cerevisiae protein kinase C (PKC1), gave enhanced secretion of most recombinant proteins that were tested, raising the possibility that it has the universal super-secreter phenotype needed in an industrial production strain of P. pastoris.

Modified VR-CAP, Alternating With Rituximab and High-dose Cytarabine: An Effective Pre-transplant Induction Regimen for Mantle Cell Lymphoma.

BACKGROUND: Initial treatment of mantle cell lymphoma (MCL) incorporating autologous stem cell transplantation affords long-term remissions, but relapses still occur. Optimal pretransplant therapy will afford high complete response rates and not impair stem cell collection. Incorporation of bortezomib represents a natural evolution of pretransplant therapy, given its proven first-line efficacy and minimal impact on stem cell collection. PATIENTS AND METHODS: At the University of Washington/Seattle Cancer Care Alliance and the Cleveland Clinic Foundation, we developed modified VR-CAP/R+ara-C (bortezomib, rituximab, cyclophosphamide, doxorubicin, and prednisone, alternating with rituximab and high-dose cytarabine), for transplant-eligible patients with MCL. This regimen was administered as standard-of-care, pretransplant therapy to consecutive patients with MCL from April 2015 to the present. RESULTS: A total of 37 patients were treated with this regimen, including 18 at the University of Washington/Seattle Cancer Care Alliance and 19 at the Cleveland Clinic Foundation. Most patients had intermediate- or high-risk disease by both (mantle-cell lymphoma international prognostic index (MIPI)-B and MIPI-C category. Complete response to induction was achieved in 32 (86%) of 37 evaluable patients; 2 achieved partial response, and 3 had primary refractory disease. Stem cell collection was successful in 1 attempt in 30 of 32 patients. The median follow-up of survivors measured from start of treatment is 17.4 months. Five patients have progressed, and 4 have died (2 owing to lymphoma, 2 from toxicity). CONCLUSION: Modified VR-CAP/R+ara-C is feasible pretransplant therapy for patients with MCL and is associated with a high rate of complete response and eligibility for autologous stem cell transplantation.

The effect of α-mating factor secretion signal mutations on recombinant protein expression in Pichia pastoris.

The methylotrophic yeast, Pichia pastoris, has been genetically engineered to produce many heterologous proteins for industrial and research purposes. In order to secrete proteins for easier purification from the extracellular medium, the coding sequence of recombinant proteins is initially fused to the Saccharomyces cerevisiae α-mating factor secretion signal leader. Extensive site-directed mutagenesis of the prepro-region of the α-mating factor secretion signal sequence was performed in order to determine the effects of various deletions and substitutions on expression. Though some mutations clearly dampened protein expression, deletion of amino acids 57-70, corresponding to the predicted 3rd alpha helix of α-mating factor secretion signal, increased secretion of reporter proteins horseradish peroxidase and lipase at least 50% in small-scale cultures. These findings raise the possibility that the secretory efficiency of the leader can be further enhanced in the future.