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SUMMARY Along with Parkin, PINK1 plays a critical role in maintaining mitochondrial quality control. Although PINK1 is expressed constitutively, its level is kept low in healthy mitochondria by polyubiquitination and ensuing proteasomal degradation of its mature, 52 kDa, form. We show here that the target of PINK1 polyubiquitination is the mature form and is mediated by ubiquitination of a conserved lysine at position 137. Notably, the full-length protein also contains Lys-137 but is not ubiquitinated. On the basis of our data, we propose that cleavage of full-length PINK1 at Phe-104 disrupts the major hydrophobic membrane-spanning domain in the protein, inducing a conformation change in the resultant mature form that exposes Lys-137 to the cytosol for subsequent modification by the ubiquitination machinery. Thus, the balance between the full-length and mature PINK1 allows its levels to be regulated via ubiquitination of the mature form and ensures that PINK1 functions as a mitochondrial quality control factor., In Brief PINK1 mutations cause Parkinson’s disease. PINK1 is cleaved into a shorter 52-kDa form at the mitochondrial membrane, but regulation of the turnover of cleaved PINK1 is unknown. Liu et al. show that polyubiquitination of cleaved PINK1 regulates its degradation via the proteasome.

Maintaining a pool of functional mitochondria requires degradation of damaged ones within the cell. PINK1 is critical in this quality-control process: loss of mitochondrial membrane potential causes PINK1 to accumulate on the mitochondrial surface, triggering mitophagy. However, little is known about how PINK1 is regulated. Recently, we showed that PINK1 content is kept low in healthy mitochondria by continuous ubiquitination and proteasomal degradation of its mature form via a mechanism inconsistent with the proposed N-end rule process. Using both human female and monkey cell lines, we now demonstrate that once generated within the mitochondria, 52 kDa PINK1 adopts a mitochondrial topology most consistent with it being at the mitochondrial–endoplasmic reticulum (ER) interface. From this particular submitochondrial location, PINK1 interacts with components of the ER-associated degradation pathway, such as the E3 ligases gp78 and HRD1, which cooperate to catalyze PINK1 ubiquitination. The valosin-containing protein and its cofactor, UFD1, then target ubiquitinated PINK1 for proteasomal degradation. Our data show that PINK1 in healthy mitochondria is negatively regulated via an interplay between mitochondria and ER, and shed light on how this mitochondrial protein gains access to the proteasome. SIGNIFICANCE STATEMENT Regulation of mitochondrial content of PINK1, a contributor to mitophagy, is an important area of research. Recently, we found that PINK1 content is kept low in healthy mitochondria by continuous ubiquitination and proteasomal degradation. We now extend and refine this novel finding by showing that PINK1 localizes at the mitochondrial–endoplasmic reticulum (ER) interface, from where it interacts with the ER-associated degradation machinery, which catalyzes its ubiquitination and transfer to the proteasome. Thus, these data show that PINK1 in healthy mitochondria is negatively regulated via a mitochondria and ER interplay, and how this mitochondrial protein gains access to the proteasome.

Background School-located influenza vaccination (SLIV) programs are a promising strategy for increasing vaccination coverage among schoolchildren. However, questions of economic sustainability have dampened enthusiasm for this approach in the United States. We evaluated SLIV sustainability of a health department led, county-wide SLIV program in Alachua County, Florida. Based on Alachua's outcome data, we modeled the sustainability of SLIV programs statewide using two different implementation costs and at different vaccination rates, reimbursement amount, and Vaccines for Children (VFC) coverage. Methods Mass vaccination clinics were conducted at 69 Alachua County schools in 2013 using VFC (for Medicaid and uninsured children) and non-VFC vaccines. Claims were processed after each clinic and submitted to insurance providers for reimbursement ($5 Medicaid and $47.04 from private insurers). We collected programmatic expenditures and volunteer hours to calculate fixed and variable costs for two different implementation costs (with or without in-kind costs included). We project program sustainability for Florida using publicly available county-specific student populations and health insurance enrollment data. Results Approximately 42% (n = 12,853) of pre-kindergarten – 12th grade students participated in the SLIV program in Alachua. Of the 13,815 doses provided, 58% (8042) were non-VFC vaccine. Total implementation cost was $14.95/dose or $7.93/dose if “in-kind” costs were not included. The program generated a net surplus of $24,221, despite losing $4.68 on every VFC dose provided to Medicaid and uninsured children. With volunteers, 99% of Florida counties would be sustainable at a 50% vaccination rate and average reimbursement amount of $3.25 VFC and $37 non-VFC. Without volunteers, 69% of counties would be sustainable at 50% vaccination rate if all VFC recipients were on Medicaid and its reimbursement increased from $5 to $10 (amount private practices receive). Conclusions and relevance Key factors that contributed to the sustainability and success of an SLIV program are: targeting privately insured children and reducing administration cost through volunteers. Counties with a high proportion of VFC eligible children may not be sustainable without subsidies at $5 Medicaid reimbursement.