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Photodynamic therapy (PDT) is a modality of cancer treatment in which tumor cells are destroyed by reactive oxygen species (ROS) produced by photosensitizers following its activation with visible or near infrared light. The PDT success is dependent on different factors namely on the efficiency of the photosensitizer deliver and targeting ability. In this review a special attention will be given to the role of some drug delivery systems to improve the efficiency of tetrapyrrolic photosensitizers to this type of treatment.

Infertility is a growing concern in modern society, with 30% of cases being due to male factors, namely reduced sperm concentration, decreased motility and abnormal morphology. Sperm cells are highly compartmentalized, almost devoid of transcription and translation consequently processes such as protein phosphorylation provide a key general mechanism for regulating vital cellular functions, more so than for undifferentiated cells. Reversible protein phosphorylation is the principal mechanism regulating most physiological processes in eukaryotic cells. To date, hundreds of protein kinases have been identified, but significantly fewer phosphatases (PPs) are responsible for counteracting their action. This discrepancy can be explained in part by the mechanism used to control phosphatase activity, which is based on regulatory interacting proteins. This is particularly true for PP1, a major serine/threonine-PP, for which >200 interactors (PP1 interacting proteins-PIPs) have been indentified that control its activity, subcellular location and substrate specificity. For PP1, several isoforms have been described, among them PP1γ2, a testis/sperm-enriched PP1 isoform. Recent findings support our hypothesis that PP1γ2 is involved in the regulation of sperm motility. This review summarizes the known sperm-specific PP1-PIPs, involved in the acquisition of mammalian sperm motility. The complexes that PP1 routinely forms with different proteins are addressed and the role of PP1/A-kinase anchoring protein complexes in sperm motility is considered. Furthermore, the potential relevance of targeting PP1-PIPs complexes to infertility diagnostics and therapeutics as well as to male contraception is also discussed.

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The trend in parenthood at an older age is increasing for both men and women in developed countries, raising concerns about the reproductive ability and the consequences for the offspring's health. While reproductive activity in women stops with menopause, a complete cessation of the reproductive potential does not occur in men. Although several studies have been published on the effects of aging on semen parameters and spermatozoa DNA integrity, literature on impact of aging on the testis, particularly cellular and molecular alterations, has been, so far, limited and controversial. This work discusses the current knowledge on testicular aging in humans and other mammals, covering topics from tissue ultrastructure, to cellular and molecular alterations. Aging affects male reproductive function at multiple levels, from sperm production and quality, to the morphology and histology of the male reproductive system. The morphological and functional changes that occur in the testes result in variations in the levels of many hormones, changes in molecules involved in mitochondrial function, receptors and signaling proteins. Despite knowing that these age-related alterations occur, their real impact on male fertility and reproductive health are still far from being fully understood, highlighting that research in the field is crucial.

Nek2 is a cell cycle-regulated serine/threonine protein kinase that is up-regulated in human cancers. Functionally, it is implicated in control of centrosome separation and bipolar spindle formation in mitotic cells and chromatin condensation in meiotic cells. Two major splice variants have been described in vertebrates, Nek2A and Nek2B, that differ in their non-catalytic C termini. Recently, a third splice variant, Nek2C, was identified that lacks an eight-amino acid internal sequence within the C-terminal domain of Nek2A. This excision occurs at the same position as the Nek2A/Nek2B splice point. As predicted from their high degree of similarity, we show here that Nek2C shares many properties with Nek2A including kinase activity, dimerization, protein phosphatase 1 interaction, mitotic degradation, microtubule binding, and centrosome localization. Unexpectedly, though, the non-centrosomal pool of protein exhibits a marked difference in distribution for the three splice variants. Nek2C is mainly nuclear, Nek2B is mainly cytoplasmic, and Nek2A is evenly distributed within nuclei and cytoplasm. Mutagenesis experiments revealed a functional bipartite nuclear localization sequence (NLS) that spans the splice site leading to Nek2C having a strong NLS, Nek2A having a weak NLS, and Nek2B having no NLS. Finally, we identified a 28-kDa protein in nuclear extracts as a potential novel substrate of Nek2. Thus, alternative splicing provides an unusual mechanism for modulating Nek2 localization, enabling it to have both nuclear and cytoplasmic functions.

Protein phosphorylation is a major regulatory mechanism of signal transduction cascades in eukaryotic cells, catalysed by kinases and reversed by protein phosphatases (PPs). Sequencing of entire genomes has revealed that ~3% of all eukaryotic genes encode kinases or PPs. Surprisingly, there appear to be 2-5 times fewer PPs than kinases. Over the past two decades it has become apparent that the diversity of Ser/Thr-specific PPs (STPP) was achieved not only by the evolution of new catalytic subunits, but also by the ability of a single catalytic subunit to interact with multiple interacting proteins. PP1, a STPP, is involved in the control of important cellular mechanisms. Several isoforms of PP1 are known in mammals: PP1α, PP1β and PP1γ. The various isoforms are highly similar, except for the N- and C-termini. The current view is that since PPs possess exquisite specificities in vivo, the key control mechanism must reside in the nature of the PP1 Interacting Protein (PIP) to which they bind. An increasing number of PIPs have been identified that are responsible for regulating the catalytic activity of PPs. Indeed, the diversity of such PIPs explains the need for relatively few catalytic subunit types, and makes them attractive targets for pharmacological intervention. This review will summarize the PIPs identified using the Yeast Two Hybrid methodology and alternative techniques, for instance bioinformatic and proteomic approaches. Further, it compiles 129 PP1-PIP relevant physiological interactions that are well documented in the literature. Finally, the use of PIPs as therapeutic targets will be addressed.

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