Extracellular vesicles released by keratinocytes regulate melanosome maturation, melanocyte dendricity, and pigment transfer.

Extracellular vesicles (EVs) facilitate the transfer of proteins, lipids, and genetic material between cells and are recognized as an additional mechanism for sustaining intercellular communication. In the epidermis, the communication between melanocytes and keratinocytes is tightly regulated to warrant skin pigmentation. Melanocytes synthesize the melanin pigment in melanosomes that are transported along the dendrites prior to the transfer of melanin pigment to keratinocytes. EVs secreted by keratinocytes modulate pigmentation in melanocytes [(A. Lo Cicero et al., Nat. Commun. 6, 7506 (2015)]. However, whether EVs secreted by keratinocytes contribute to additional processes essential for melanocyte functions remains elusive. Here, we show that keratinocyte EVs enhance the ability of melanocytes to generate dendrites and mature melanosomes and promote their efficient transfer. Further, keratinocyte EVs carrying Rac1 induce important morphological changes, promote dendrite outgrowth, and potentiate melanin transfer to keratinocytes. Hence, in addition to modulating pigmentation, keratinocytes exploit EVs to control melanocyte plasticity and transfer capacity. These data demonstrate that keratinocyte-derived EVs, by regulating melanocyte functions, are major contributors to cutaneous pigmentation and expand our understanding of the mechanism underlying skin pigmentation via a paracrine EV-mediated communication.

The GTPase Rab8 differentially controls the long- and short-range activity of the Hedgehog morphogen gradient by regulating Hedgehog apico-basal distribution.

The Hedgehog (Hh) morphogen gradient is required for patterning during metazoan development, yet the mechanisms involved in Hh apical and basolateral release and how this influences short- and long-range target induction are poorly understood. We found that depletion of the GTPase Rab8 in Hh-producing cells induces an imbalance between the level of apically and laterally released Hh. This leads to non-cell-autonomous differential effects on the expression of Hh target genes, namely an increase in its short-range targets and a concomitant decrease in long-range targets. We further found that Rab8 regulates the endocytosis and apico-basal distribution of Ihog, a transmembrane protein known to bind to Hh and to be crucial for establishment of the Hh gradient. Our data provide new insights into morphogen gradient formation, whereby morphogen activity is functionally distributed between apically and basolaterally secreted pools.

Protein association changes in the Hedgehog signaling complex mediate differential signaling strength.

Hedgehog (Hh) is a conserved morphogen that controls cell differentiation and tissue patterning in metazoans. In Drosophila, the Hh signal is transduced from the G protein-coupled receptor Smoothened (Smo) to the cytoplasmic Hh signaling complex (HSC). How activated Smo is translated into a graded activation of the downstream pathway is still not well understood. In this study, we show that the last amino acids of the cytoplasmic tail of Smo, in combination with G protein-coupled receptor kinase 2 (Gprk2), bind to the regulatory domain of Fused (Fu) and highly activate its kinase activity. We further show that this binding induces changes in the association of Fu protein with the HSC and increases the proximity of the Fu catalytic domain to its substrate, the Costal2 kinesin. We propose a new model in which, depending on the magnitude of Hh signaling, Smo and Gprk2 modulate protein association and conformational changes in the HSC, which are responsible for the differential activation of the pathway.

Direct α-synuclein promoter transactivation by the tumor suppressor p53.

BACKGROUND: Parkinson's disease (PD) is a motor disease associated with the degeneration of dopaminergic neurons of the substantia nigra pars compacta. p53 is a major neuronal pro-apoptotic factor that is at the center of gravity of multiple physiological and pathological cascades, some of which implying several key PD-linked proteins. Since p53 is up-regulated in PD-affected brain, we have examined its ability to regulate the transcription of α-synuclein, a key protein that accumulates in PD-related Lewy bodies. RESULTS: We show that pharmacological and genetic up-regulation of p53 expression lead to a strong increase of α-synuclein protein, promoter activity and mRNA levels. Several lines of evidence indicate that this transcriptional control is due to the DNA-binding properties of p53. Firstly, p53 DNA-binding dead mutations abolish p53 regulation of α-synuclein. Secondly, the deletion of p53 responsive element from α-synuclein promoter abrogates p53-mediated α-synuclein regulation. Thirdly, gel shift and chromatin immunoprecipitation studies indicate that p53 interacts physically with α-synuclein promoter both in vitro and in a physiological context. Furthermore, we show that the depletion of endogenous p53 in cells as well as in knockout mice down-regulates α-synuclein transcription. CONCLUSIONS: Overall, we have identified α-synuclein as a new transcriptional target of p53 and delineated a cellular mechanism feeding the accumulation of toxic aggregated α-synuclein in PD. This original α-syn regulatory mechanism may be central to PD-related cell death and may lead to novel opportunities to design alternative neuroprotective strategies in PD.