Effects of Isotretinoin on Meibomian Glands.

The authors have reviewed the potential etiology and long-standing consequences of isotretinoin use in the development of dry eye symptoms in the absence of significant clinical findings. Despite the normal appearance of meibomian gland structure on meibography and minimal signs of eyelid margin inflammation, the secretory function of these glands is reduced and symptoms of dryness can greatly impact a patient's quality of life. The available literature indicates that isotretinoin's effect on the meibomian glands likely mimics its effects on the sebaceous glands of the skin in the treatment of acne. Several representative cases seen at the University of California Berkeley School of Optometry Dry Eye Clinic provide a clinical paradigm with the goal of raising awareness of the potential prevalence of this disease in patients who experience symptoms of dry eye. These cases highlight the importance of meibomian gland expression in determining whether there is poor quality and/or quantity of meibum secondary to reduced gland function. Currently, there is no definitive method to restore the structure and function of damaged meibomian glands; thus, treatment options for isotretinoin-associated meibomian gland dysfunction are primarily palliative to manage patient symptoms.

Analysis of the 5' untranslated region (5'UTR) of the alcohol oxidase 1 (AOX1) gene in recombinant protein expression in Pichia pastoris.

Pichia pastoris is a methylotrophic yeast that has been genetically engineered to express over one thousand heterologous proteins valued for industrial, pharmaceutical and basic research purposes. In most cases, the 5' untranslated region (UTR) of the alcohol oxidase 1 (AOX1) gene is fused to the coding sequence of the recombinant gene for protein expression in this yeast. Because the effect of the AOX1 5'UTR on protein expression is not known, site-directed mutagenesis was performed in order to decrease or increase the length of this region. Both of these types of changes were shown to affect translational efficiency, not transcript stability. While increasing the length of the 5'UTR clearly decreased expression of a ß-galactosidase reporter in a proportional manner, a deletion analysis demonstrated that the AOX1 5'UTR contains a complex mixture of both positive and negative cis-acting elements, suggesting that the construction of a synthetic 5'UTR optimized for a higher level of expression may be challenging.

An improved method for enhanced production and biological activity of human secretory leukocyte protease inhibitor (SLPI) in Pichia pastoris.

The human secretory leukocyte protease inhibitor (SLPI) is an 11.7 kD cysteine-rich protein that has been shown to possess anti-protease, anti-inflammatory, and antimicrobial properties. By using a Pichia pastoris strain that overproduces protein disulfide isomerase (PDI), we obtained greater than fivefold higher levels of SLPI than in strains expressing normal levels of PDI and containing multiple copies of the SLPI gene. Elevated levels of PDI also enhanced the specific activity of the secreted SLPI by helping it achieve a proper tertiary structure. Mass spectrometry analysis indicated a greater number of disulfide bonds in the SLPI produced by the PDI overexpression strain compared to the SLPI produced in strains with normal PDI levels. Although others have utilized a similar strategy to increase yield, we believe that this is the first example of PDI overexpression being demonstrated to enhance the folding and thus increase the biological activity of a protein produced in the yeast P. pastoris.

Expression and characterization of recombinant human secretory leukocyte protease inhibitor (SLPI) protein from Pichia pastoris.

The human secretory leukocyte protease inhibitor (SLPI) has been shown to possess anti-protease, anti-inflammatory and antimicrobial properties. Its presence in saliva is believed to be a major deterrent to oral transmission of human immunodeficiency virus-1. The 11.7kDa peptide is a secreted, nonglycosylated protein rich in disulfide bonds. Currently, recombinant SLPI is only available as an expensive bacterial expression product. We have investigated the utility of the methylotrophic yeast Pichia pastoris to produce and secrete SLPI with C-terminal c-myc and polyhistidine tags. The post-transformational vector amplification protocol was used to isolate strains with increased copy number, and culturing parameters were varied to optimize SLPI expression. Modification of the purification procedure allowed the secreted, recombinant protein to be isolated from the cell-free fermentation medium with cobalt affinity chromatography. This yeast-derived SLPI was shown to have an anti-protease activity comparable to the commercially available bacterial product. Thus, P. pastoris provides an efficient, cost-effective system for producing SLPI for structure function analysis studies as well as a wide array of potential therapeutic applications.

Direct selection of Pichia pastoris expression strains using new G418 resistance vectors.

The methylotrophic yeast, Pichia pastoris, is widely used as a host organism for the expression of heterologous proteins. Currently, the Zeocin and blasticidin resistance genes are the only dominant selectable markers that can be used for primary selection of transformants. In this report we describe new expression vectors that can be used to select directly for P. pastoris transformants using G418 resistance conferred by a modified Tn903kan(r) gene. Compared to other dominant markers, this system is more economical and offers a higher transformation efficiency, due to the small sizes of the cloning vectors, pKAN B and pKANalpha B (GenBank Accession Nos EU285585 and EU285586, respectively). Additionally, multicopy transformants can be generated using these new vectors.