Steroid 21-hydroxylase expression and activity in human lymphocytes

Area of Science:

• Endocrinology
• Genetics
• Immunology

Background:

• Steroid 21-hydroxylase, encoded by CYP21, is primarily known for its expression in the adrenal cortex.
• Mutations in CYP21 lead to congenital adrenal hyperplasia (CAH), a serious condition.
• Previous research hinted at alternative sources of 21-hydroxylase activity beyond the adrenal glands.

Purpose of the Study:

• To investigate novel sources of 21-hydroxylase expression.
• To determine if human B lymphocytes express CYP21.
• To explore the functional implications of non-adrenal 21-hydroxylase activity in CAH.

Main Methods:

• Analysis of CYP21 transcript levels in cultured human B lymphocytes from healthy individuals and CAH patients.
• Detection of CYP21 transcript in B cell lines from CAH subjects with varying CYP21 mutations, including homozygous deletion.
• Enzymatic assays on cultured lymphoid cells and peripheral blood leukocytes to assess 21-hydroxylase activity.

Main Results:

• A novel source of CYP21 expression was identified in normal human cultured B lymphocytes.
• Reduced CYP21 transcript levels were observed in B cell lines from CAH subjects compared to normal controls.
• No CYP21 transcript was detected in lymphocytes from a CAH patient with a homozygous CYP21 deletion.
• Cultured lymphoid cells and peripheral blood leukocytes demonstrated 21-hydroxylase activity, converting key steroid precursors.
• This activity was present even in cells lacking CYP21, indicating the presence of an alternative isozyme.

Conclusions:

• Human lymphocytes express CYP21, providing a potential alternative source of this enzyme.
• Lymphocytes possess a distinct 21-hydroxylase isozyme separate from CYP21.
• The activity of this lymphocyte-associated isozyme may offer partial compensation for severe adrenal 21-hydroxylase deficiency in CAH.