The thyroperoxidase doublet is not produced by alternative splicing

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• Thyroid peroxidase (TPO) is crucial for thyroid hormone synthesis.
• TPO exists as a full-length transcript (TPO1) and shorter variants, including TPO2.
• TPO typically appears as a 105-110 kDa doublet on Western blots, but the origin is unclear.

Purpose of the Study:

• To investigate whether the TPO doublet arises from the translation of the TPO2 transcript.
• To develop specific antibodies against unique TPO1 and TPO2 splice junction sequences.
• To analyze TPO protein expression in normal and Graves' thyroid tissue.

Main Methods:

• Production of recombinant fusion proteins for unique TPO1 and TPO2 peptide segments.
• Generation of specific polyclonal antibodies against these fusion proteins in rabbits.
• Western blot analysis of thyroid membranes using polyclonal and monoclonal antibodies under reducing and non-reducing conditions.

Main Results:

• Specific polyclonal antibodies were successfully generated against TPO1 and TPO2 peptide segments.
• Western blots showed a consistent 105-110 kDa doublet for TPO under non-reducing conditions, resolving into distinct 105 and 110 kDa bands under reducing conditions.
• This pattern was identical across all antibodies tested, in both normal and Graves' thyroid tissue.

Conclusions:

• The TPO doublet observed in Western blots is not a result of TPO2 transcript translation.
• The doublet likely represents post-translational modifications of the TPO protein.
• Alternative splicing to TPO2 does not contribute to the observed TPO protein forms.